Prokaryotic Initiation Factors
Prokaryotic Initiation Factor-1
Peptide Initiation Factors
Prokaryotic Initiation Factor-3
Prokaryotic Initiation Factor-2
Prokaryotic Cells
Eukaryotic Initiation Factors
Eukaryotic Initiation Factor-2
Eukaryotic Initiation Factor-4E
Eukaryotic Initiation Factor-3
Peptide Chain Initiation, Translational
Eukaryotic Initiation Factor-4G
Protein Biosynthesis
Eukaryotic Initiation Factor-4A
Eukaryotic Initiation Factor-4F
Ribosomes
Eukaryotic Initiation Factor-1
Molecular Sequence Data
Eukaryotic Initiation Factor-2B
RNA, Transfer, Met
Reticulocytes
Leaderless mRNAs bind 70S ribosomes more strongly than 30S ribosomal subunits in Escherichia coli. (1/21)
By primer extension inhibition assays, 70S ribosomes bound with higher affinity, or stability, than did 30S subunits to leaderless mRNAs containing AUG or GUG start codons. Addition of translation initiation factors affected ribosome binding to leaderless mRNAs. Our results suggest that translation of leaderless mRNAs might initiate through a pathway involving 70S ribosomes or 30S subunits lacking IF3. (+info)The genetic core of the universal ancestor. (2/21)
Molecular analysis of conserved sequences in the ribosomal RNAs of modern organisms reveals a three-domain phylogeny that converges in a universal ancestor for all life. We used the Clusters of Orthologous Groups database and information from published genomes to search for other universally conserved genes that have the same phylogenetic pattern as ribosomal RNA, and therefore constitute the ancestral genetic core of cells. Our analyses identified a small set of genes that can be traced back to the universal ancestor and have coevolved since that time. As indicated by earlier studies, almost all of these genes are involved with the transfer of genetic information, and most of them directly interact with the ribosome. Other universal genes have either undergone lateral transfer in the past, or have diverged so much in sequence that their distant past could not be resolved. The nature of the conserved genes suggests innovations that may have been essential to the divergence of the three domains of life. The analysis also identified several genes of unknown function with phylogenies that track with the ribosomal RNA genes. The products of these genes are likely to play fundamental roles in cellular processes. (+info)Preferential translation of cold-shock mRNAs during cold adaptation. (3/21)
Upon temperature downshift below the lower threshold of balanced growth (approximately 20 degrees C), the Escherichia coli translational apparatus undergoes modifications allowing the selective translation of the transcripts of cold shock-induced genes, while bulk protein synthesis is drastically reduced. Here we were able to reproduce this translational bias in E. coli cell-free extracts prepared at various times during cold adaptation which were found to display different capacities to translate different types of mRNAs as a function of temperature. Several causes were found to contribute to the cold-shock translational bias: Cold-shock mRNAs contain cis-elements, making them intrinsically more prone to being translated in the cold, and they are selective targets for trans-acting factors present in increased amounts in the translational apparatus of cold-shocked cells. CspA was found to be among these trans-acting factors. In addition to inducing a higher level of CspA, cold shock was found to cause a strong (two- to threefold) stoichiometric imbalance of the ratio between initiation factors (IF1, IF2, IF3) and ribosomes without altering the stoichiometric ratio between the factors themselves. The most important sources of cold-shock translational bias is IF3, which strongly and selectively favors translation of cold-shock mRNAs in the cold. IF1 and the RNA chaperone CspA, which stimulate translation preferentially in the cold without mRNA selectivity, can also contribute to the translational bias. Finally, in contrast to a previous claim, translation of cold-shock cspA mRNA in the cold was found to be as sensitive as that of a non-cold-shock mRNA to both chloramphenicol and kanamycin inhibition. (+info)Isolation and characterization of ribosomes and translation initiation factors from the gram-positive soil bacterium Streptomyces lividans. (4/21)
A primer extension inhibition (toeprint) assay was developed using ribosomes and ribosomal subunits from Streptomyces lividans. This assay allowed the study of ribosome binding to streptomycete leaderless and leadered mRNA. Purified 30S subunits were unable to form a ternary complex on aph leaderless mRNA, whereas 70S ribosomes could form ternary complexes on this mRNA. 30S subunits formed ternary complexes on leadered aph and malE mRNA. The translation initiation factors (IF1, IF2, and IF3) from S. lividans were isolated and included in toeprint and filter binding assays with leadered and leaderless mRNA. Generally, the IFs reduced the toeprint signal on leadered mRNA; however, incubation of IF1 and IF2 with 30S subunits that had been washed under high-salt conditions promoted the formation of a ternary complex on aph leaderless mRNA. Our data suggest that, as reported for Escherichia coli, initiation complexes with leaderless mRNAs might use a novel pathway involving 70S ribosomes or 30S subunits bound by IF1 and IF2 but not IF3. Some mRNA-ribosome-initiator tRNA reactions that yielded weak or no toeprint signals still formed complexes in filter binding assays, suggesting the occurrence of interactions that are not stable in the toeprint assay. (+info)Oligo kernels for datamining on biological sequences: a case study on prokaryotic translation initiation sites. (5/21)
BACKGROUND: Kernel-based learning algorithms are among the most advanced machine learning methods and have been successfully applied to a variety of sequence classification tasks within the field of bioinformatics. Conventional kernels utilized so far do not provide an easy interpretation of the learnt representations in terms of positional and compositional variability of the underlying biological signals. RESULTS: We propose a kernel-based approach to datamining on biological sequences. With our method it is possible to model and analyze positional variability of oligomers of any length in a natural way. On one hand this is achieved by mapping the sequences to an intuitive but high-dimensional feature space, well-suited for interpretation of the learnt models. On the other hand, by means of the kernel trick we can provide a general learning algorithm for that high-dimensional representation because all required statistics can be computed without performing an explicit feature space mapping of the sequences. By introducing a kernel parameter that controls the degree of position-dependency, our feature space representation can be tailored to the characteristics of the biological problem at hand. A regularized learning scheme enables application even to biological problems for which only small sets of example sequences are available. Our approach includes a visualization method for transparent representation of characteristic sequence features. Thereby importance of features can be measured in terms of discriminative strength with respect to classification of the underlying sequences. To demonstrate and validate our concept on a biochemically well-defined case, we analyze E. coli translation initiation sites in order to show that we can find biologically relevant signals. For that case, our results clearly show that the Shine-Dalgarno sequence is the most important signal upstream a start codon. The variability in position and composition we found for that signal is in accordance with previous biological knowledge. We also find evidence for signals downstream of the start codon, previously introduced as transcriptional enhancers. These signals are mainly characterized by occurrences of adenine in a region of about 4 nucleotides next to the start codon. CONCLUSIONS: We showed that the oligo kernel can provide a valuable tool for the analysis of relevant signals in biological sequences. In the case of translation initiation sites we could clearly deduce the most discriminative motifs and their positional variation from example sequences. Attractive features of our approach are its flexibility with respect to oligomer length and position conservation. By means of these two parameters oligo kernels can easily be adapted to different biological problems. (+info)Selenocysteine tRNA-specific elongation factor SelB is a structural chimaera of elongation and initiation factors. (6/21)
In all three kingdoms of life, SelB is a specialized translation elongation factor responsible for the cotranslational incorporation of selenocysteine into proteins by recoding of a UGA stop codon in the presence of a downstream mRNA hairpin loop. Here, we present the X-ray structures of SelB from the archaeon Methanococcus maripaludis in the apo-, GDP- and GppNHp-bound form and use mutational analysis to investigate the role of individual amino acids in its aminoacyl-binding pocket. All three SelB structures reveal an EF-Tu:GTP-like domain arrangement. Upon binding of the GTP analogue GppNHp, a conformational change of the Switch 2 region in the GTPase domain leads to the exposure of SelB residues involved in clamping the 5' phosphate of the tRNA. A conserved extended loop in domain III of SelB may be responsible for specific interactions with tRNA(Sec) and act as a ruler for measuring the extra long acceptor arm. Domain IV of SelB adopts a beta barrel fold and is flexibly tethered to domain III. The overall domain arrangement of SelB resembles a 'chalice' observed so far only for initiation factor IF2/eIF5B. In our model of SelB bound to the ribosome, domain IV points towards the 3' mRNA entrance cleft ready to interact with the downstream secondary structure element. (+info)Structural basis for the function of the ribosomal L7/12 stalk in factor binding and GTPase activation. (7/21)
The L7/12 stalk of the large subunit of bacterial ribosomes encompasses protein L10 and multiple copies of L7/12. We present crystal structures of Thermotoga maritima L10 in complex with three L7/12 N-terminal-domain dimers, refine the structure of an archaeal L10E N-terminal domain on the 50S subunit, and identify these elements in cryo-electron-microscopic reconstructions of Escherichia coli ribosomes. The mobile C-terminal helix alpha8 of L10 carries three L7/12 dimers in T. maritima and two in E. coli, in concordance with the different length of helix alpha8 of L10 in these organisms. The stalk is organized into three elements (stalk base, L10 helix alpha8-L7/12 N-terminal-domain complex, and L7/12 C-terminal domains) linked by flexible connections. Highly mobile L7/12 C-terminal domains promote recruitment of translation factors to the ribosome and stimulate GTP hydrolysis by the ribosome bound factors through stabilization of their active GTPase conformation. (+info)An extrasynaptic GABAA receptor mediates tonic inhibition in thalamic VB neurons. (8/21)
Whole cell patch-clamp recordings were obtained from thalamic ventrobasal (VB) and reticular (RTN) neurons in mouse brain slices. A bicuculline-sensitive tonic current was observed in VB, but not in RTN, neurons; this current was increased by the GABA(A) receptor agonist 4,5,6,7-tetrahydroisothiazolo-[5,4-c]pyridine-3-ol (THIP; 0.1 microM) and decreased by Zn(2+) (50 microM) but was unaffected by zolpidem (0.3 microM) or midazolam (0.2 microM). The pharmacological profile of the tonic current is consistent with its generation by activation of GABA(A) receptors that do not contain the alpha(1) or gamma(2) subunits. GABA(A) receptors expressed in HEK 293 cells that contained alpha(4)beta(2)delta subunits showed higher sensitivity to THIP (gaboxadol) and GABA than did receptors made up from alpha(1)beta(2)delta, alpha(4)beta(2)gamma(2s,) or alpha(1)beta(2)gamma(2s) subunits. Western blot analysis revealed that there is little, if any, alpha(3) or alpha(5) subunit protein in VB. In addition, co-immunoprecipitation studies showed that antibodies to the delta subunit could precipitate alpha(4), but not alpha(1) subunit protein. Confocal microscopy of thalamic neurons grown in culture confirmed that alpha(4) and delta subunits are extensively co-localized with one another and are found predominantly, but not exclusively, at extrasynaptic sites. We conclude that thalamic VB neurons express extrasynaptic GABA(A) receptors that are highly sensitive to GABA and THIP and that these receptors are most likely made up of alpha(4)beta(2)delta subunits. In view of the critical role of thalamic neurons in the generation of oscillatory activity associated with sleep, these receptors may represent a principal site of action for the novel hypnotic agent gaboxadol. (+info)Prokaryotic initiation factors are a group of proteins that play an essential role in the initiation phase of protein synthesis in prokaryotes, such as bacteria. These factors help to assemble the ribosome complex and facilitate the binding of messenger RNA (mRNA) and transfer RNA (tRNA) during the start of translation, the process by which genetic information encoded in mRNA is converted into a protein sequence.
There are three main prokaryotic initiation factors:
1. IF1 (InfA): This factor binds to the 30S ribosomal subunit and prevents it from prematurely binding to the 50S ribosomal subunit before the mRNA is properly positioned. It also helps in the correct positioning of the initiator tRNA (tRNAi) during initiation.
2. IF2 (InfB): This factor plays a crucial role in recognizing and binding the initiator tRNA to the 30S ribosomal subunit, forming the 70S initiation complex. It also hydrolyzes GTP during this process, which provides energy for the reaction.
3. IF3 (InfC): This factor helps in the dissociation of the 70S ribosome into its individual 30S and 50S subunits after translation is complete. During initiation, it binds to the 30S subunit and prevents incorrect mRNA binding while promoting the correct positioning of the initiator tRNA.
These prokaryotic initiation factors work together to ensure accurate and efficient protein synthesis in bacteria and other prokaryotes.
The Prokaryotic Initiation Factor-1 (IF-1) is a bacterial protein involved in the initiation phase of protein synthesis. It plays a crucial role in the formation of the 70S initiation complex, which is a prerequisite for the beginning of translation. Specifically, IF-1 associates with the 30S ribosomal subunit and helps to position the initiator tRNA (tRNA^fmet^) in the P site during the formation of the initiation complex. This process is essential for the accurate start of protein synthesis in prokaryotic organisms. IF-1 is also known as IF-1A or infA, and its gene is located in the bacterial chromosome.
Peptide initiation factors are a group of proteins involved in the process of protein synthesis in cells, specifically during the initial stage of elongation called initiation. In this phase, they assist in the assembly of the ribosome, an organelle composed of ribosomal RNA and proteins, at the start codon of a messenger RNA (mRNA) molecule. This marks the beginning of the translation process where the genetic information encoded in the mRNA is translated into a specific protein sequence.
There are three main peptide initiation factors in eukaryotic cells:
1. eIF-2 (eukaryotic Initiation Factor 2): This factor plays a crucial role in binding methionyl-tRNAi, the initiator tRNA, to the small ribosomal subunit. It does so by forming a complex with GTP and the methionyl-tRNAi, which then binds to the 40S ribosomal subunit. Once bound, eIF-2-GTP-Met-tRNAi recognizes the start codon (AUG) on the mRNA.
2. eIF-3: This is a large multiprotein complex that interacts with both the small and large ribosomal subunits and helps stabilize their interaction during initiation. It also plays a role in recruiting other initiation factors to the preinitiation complex.
3. eIF-4F: This factor is a heterotrimeric protein complex consisting of eIF-4A (an ATP-dependent RNA helicase), eIF-4E (which binds the m7G cap structure at the 5' end of most eukaryotic mRNAs), and eIF-4G (a scaffolding protein that bridges interactions between eIF-4A, eIF-4E, and other initiation factors). eIF-4F helps unwind secondary structures in the 5' untranslated region (5' UTR) of mRNAs, promoting efficient recruitment of the 43S preinitiation complex to the mRNA.
Together, these peptide initiation factors facilitate the recognition of the correct start codon and ensure efficient translation initiation in eukaryotic cells.
The Prokaryotic Initiation Factor-3 (IF3) is a protein factor involved in the initiation phase of protein synthesis in prokaryotic organisms, such as bacteria. Specifically, IF3 plays a crucial role in the accurate selection and binding of initiator tetra codon (AUG) during the formation of the initiation complex on the small ribosomal subunit.
In prokaryotes, protein synthesis begins with the formation of a 30S initiation complex, which consists of the 30S ribosomal subunit, initiator tRNA (tRNA^fMet^), mRNA, and various initiation factors, including IF3. The primary function of IF3 is to prevent non-initiator tRNAs from binding to the P site on the 30S ribosomal subunit, ensuring that only the initiator tRNA can bind to the correct start codon (AUG) during initiation.
IF3 has two distinct domains: an N-terminal domain responsible for interacting with the 30S ribosomal subunit and a C-terminal domain involved in binding to the initiator tRNA. After the formation of the 30S initiation complex, IF3 is released from the complex following the hydrolysis of GTP by another initiation factor (IF2). This release allows for the joining of the large ribosomal subunit and the beginning of elongation phase of protein synthesis.
In summary, Prokaryotic Initiation Factor-3 is a critical player in prokaryotic translation, ensuring accurate initiation by promoting the binding of initiator tRNA to the correct start codon on the small ribosomal subunit.
Prokaryotic Initiation Factor-2 (IF-2) is a protein factor that plays an essential role in the initiation phase of protein synthesis in prokaryotes. It is involved in the binding of the small 30S ribosomal subunit to the initiator tRNA (tRNA^fMet or tRNA^met) and mRNA, forming the 30S initiation complex. This factor aids in positioning the initiator tRNA at the correct start codon (AUG) on the mRNA, thereby facilitating the accurate initiation of translation. IF-2 is one of three initiation factors (IF-1, IF-2, and IF-3) that are required for the initiation phase of protein synthesis in prokaryotes.
Prokaryotic cells are simple, single-celled organisms that do not have a true nucleus or other membrane-bound organelles. They include bacteria and archaea. The genetic material of prokaryotic cells is composed of a single circular chromosome located in the cytoplasm, along with small, circular pieces of DNA called plasmids. Prokaryotic cells have a rigid cell wall, which provides protection and support, and a flexible outer membrane that helps them to survive in diverse environments. They reproduce asexually by binary fission, where the cell divides into two identical daughter cells. Compared to eukaryotic cells, prokaryotic cells are generally smaller and have a simpler structure.
Eukaryotic initiation factors (eIFs) are a group of proteins that play a crucial role in the process of protein synthesis, also known as translation, in eukaryotic cells. During the initiation phase of translation, these factors help to assemble the necessary components for the formation of the initiation complex on the small ribosomal subunit and facilitate the recruitment of messenger RNA (mRNA) and the transfer RNA carrying the initiator methionine (tRNAi^Met).
There are several eukaryotic initiation factors, each with a specific function in the initiation process. Some of the key eIFs include:
1. eIF1: helps to maintain the correct conformation of the 40S ribosomal subunit and prevents premature binding of tRNAi^Met.
2. eIF1A: stabilizes the interaction between eIF1 and the 40S ribosomal subunit, and also promotes the recruitment of tRNAi^Met.
3. eIF2: forms a ternary complex with GTP and tRNAi^Met, which binds to the 40S ribosomal subunit in an AUG-specific manner.
4. eIF3: interacts with the 40S ribosomal subunit and helps to recruit other initiation factors, including eIF1, eIF1A, and eIF2.
5. eIF4F: a heterotrimeric complex that includes eIF4E (cap-binding protein), eIF4A (DEAD-box RNA helicase), and eIF4G (scaffolding protein). This complex recognizes the 5' cap structure of mRNAs and facilitates their recruitment to the ribosome.
6. eIF5: promotes the hydrolysis of GTP in the eIF2-GTP-tRNAi^Met ternary complex, leading to the dissociation of eIF2-GDP and the formation of a stable 43S preinitiation complex.
7. eIF5B: catalyzes the joining of the 60S ribosomal subunit to form an 80S initiation complex and facilitates the release of eIF1A, eIF2-GDP, and eIF5 from the complex.
These initiation factors play crucial roles in ensuring accurate translation initiation, maintaining translational fidelity, and regulating gene expression at the level of translation. Dysregulation of these processes can lead to various human diseases, including cancer, neurodegenerative disorders, and viral infections.
Eukaryotic Initiation Factor-2 (eIF-2) is a crucial protein complex in the process of protein synthesis, also known as translation, in eukaryotic cells. It plays a role in the initiation phase of translation, where it helps to recruit and position the initiator tRNA (tRNAiMet) at the start codon on the mRNA molecule.
The eIF-2 complex is made up of three subunits: α, β, and γ. Phosphorylation of the α subunit (eIF-2α) plays a regulatory role in protein synthesis. When eIF-2α is phosphorylated by one of several eIF-2 kinases in response to various stress signals, it leads to a decrease in global protein synthesis, allowing the cell to conserve resources and survive during times of stress. This process is known as the integrated stress response (ISR).
In summary, Eukaryotic Initiation Factor-2 (eIF-2) is a protein complex that plays a critical role in the initiation phase of protein synthesis in eukaryotic cells, and its activity can be regulated by phosphorylation of the α subunit.
Eukaryotic Initiation Factor-4E (eIF4E) is a protein that plays a crucial role in the initiation phase of protein synthesis in eukaryotic cells. It is a subunit of the eIF4F complex, which also includes eIF4A and eIF4G proteins.
The primary function of eIF4E is to recognize and bind to the 5' cap structure (m7GpppN) of messenger RNA (mRNA), a modified guanine nucleotide that is added to the 5' end of mRNA during transcription. This binding event helps recruit other initiation factors, including eIF4A and eIF4G, to form the eIF4F complex, which subsequently binds to the small ribosomal subunit and promotes the scanning of the 5' untranslated region (5' UTR) of mRNA for the start codon (AUG).
The activity of eIF4E is tightly regulated through various post-translational modifications, such as phosphorylation, and interactions with other regulatory proteins. Dysregulation of eIF4E has been implicated in several human diseases, including cancer, where increased eIF4E expression and activity have been associated with poor prognosis and resistance to therapy.
Eukaryotic Initiation Factor-3 (eIF-3) is a multi-subunit protein complex that plays a crucial role in the initiation phase of eukaryotic translation, the process by which genetic information encoded in mRNA is translated into proteins. Specifically, eIF-3 is involved in the assembly of the 43S preinitiation complex (43S PIC), which includes the small ribosomal subunit, various initiation factors, and methionyl-tRNAi (met-tRNAi).
The eIF-3 complex consists of at least 12 different subunits, designated as eIF-3a through eIF-3m. These subunits are believed to play a role in regulating the assembly and disassembly of the 43S PIC, promoting the scanning of mRNA for initiation codons, and facilitating the recruitment of the large ribosomal subunit during translation initiation.
Dysregulation of eIF-3 function has been implicated in various human diseases, including cancer, neurodegenerative disorders, and viral infections. Therefore, understanding the molecular mechanisms underlying eIF-3 function is an important area of research with potential implications for the development of novel therapeutic strategies.
Peptide chain initiation in translational terms refers to the process by which the synthesis of a protein begins on a ribosome. This is the first step in translation, where the small ribosomal subunit binds to an mRNA molecule at the start codon (usually AUG), bringing with it the initiator tRNA charged with a specific amino acid (often N-formylmethionine in prokaryotes or methionine in eukaryotes). The large ribosomal subunit then joins this complex, forming a functional initiation complex. This marks the beginning of the elongation phase, where subsequent amino acids are added to the growing peptide chain until termination is reached.
Eukaryotic Initiation Factor-4G (eIF4G) is a large protein in eukaryotic cells that plays a crucial role in the initiation phase of protein synthesis, also known as translation. It serves as a scaffold or platform that brings together various components required for the assembly of the translation initiation complex.
The eIF4G protein interacts with several other proteins involved in translation initiation, including eIF4E, eIF4A, and the poly(A)-binding protein (PABP). The binding of eIF4G to eIF4E helps recruit the methionine initiator tRNA (tRNAiMet) to the 5' cap structure of mRNA, while its interaction with eIF4A promotes the unwinding of secondary structures in the 5' untranslated region (5' UTR) of mRNA. The association of eIF4G with PABP at the 3' poly(A) tail of mRNA facilitates circularization of the mRNA, promoting efficient translation initiation and recycling of ribosomes.
There are multiple isoforms of eIF4G in eukaryotic cells, such as eIF4GI and eIF4GII, which share structural similarities but may have distinct functions or interact with different sets of proteins during the translation process. Dysregulation of eIF4G function has been implicated in various human diseases, including cancer and neurological disorders.
Protein biosynthesis is the process by which cells generate new proteins. It involves two major steps: transcription and translation. Transcription is the process of creating a complementary RNA copy of a sequence of DNA. This RNA copy, or messenger RNA (mRNA), carries the genetic information to the site of protein synthesis, the ribosome. During translation, the mRNA is read by transfer RNA (tRNA) molecules, which bring specific amino acids to the ribosome based on the sequence of nucleotides in the mRNA. The ribosome then links these amino acids together in the correct order to form a polypeptide chain, which may then fold into a functional protein. Protein biosynthesis is essential for the growth and maintenance of all living organisms.
Eukaryotic Initiation Factor-4A (eIF4A) is a type of protein involved in the process of gene expression in eukaryotic cells. More specifically, it is an initiation factor that plays a crucial role in the beginning stages of translation, which is the process by which the genetic information contained within messenger RNA (mRNA) molecules is translated into proteins.
eIF4A is a member of the DEAD-box family of RNA helicases, which are enzymes that use ATP to unwind and remodel RNA structures. In the context of translation, eIF4A helps to unwind secondary structures in the 5' untranslated region (5' UTR) of mRNAs, allowing the ribosome to bind and initiate translation.
eIF4A typically functions as part of a larger complex called eIF4F, which also includes eIF4E and eIF4G. Together, these proteins help to recruit the ribosome to the mRNA and facilitate the initiation of translation. Dysregulation of eIF4A and other initiation factors has been implicated in various diseases, including cancer.
Eukaryotic Initiation Factor-4F (eIF4F) is a multi-subunit protein complex that plays a crucial role in the initiation phase of eukaryotic mRNA translation. It is involved in the recognition and binding of the 5' cap structure (m7GpppN) of mRNA, which is a characteristic feature of eukaryotic messenger RNAs.
The eIF4F complex consists of three main subunits:
1. eIF4E: This is the cap-binding protein that directly recognizes and binds to the 5' cap structure of mRNA.
2. eIF4A: This is an RNA helicase that unwinds secondary structures in the 5' untranslated region (UTR) of mRNA, allowing for the assembly of the translation initiation complex.
3. eIF4G: This is a scaffolding protein that binds to both eIF4E and eIF4A, as well as other proteins involved in translation initiation, such as poly(A)-binding protein (PABP) and eIF3.
The formation of the eIF4F complex facilitates the recruitment of the small ribosomal subunit to the 5' end of mRNA, followed by scanning along the 5' UTR until an initiation codon (usually AUG) is encountered. Upon recognition of the initiation codon, the large ribosomal subunit joins the complex, forming a functional 80S ribosome that can engage in elongation and ultimately synthesize the protein product.
Dysregulation of eIF4F components has been implicated in various human diseases, including cancer, viral infection, and neurological disorders.
Ribosomes are complex macromolecular structures composed of ribonucleic acid (RNA) and proteins that play a crucial role in protein synthesis within cells. They serve as the site for translation, where messenger RNA (mRNA) is translated into a specific sequence of amino acids to create a polypeptide chain, which eventually folds into a functional protein.
Ribosomes consist of two subunits: a smaller subunit and a larger subunit. These subunits are composed of ribosomal RNA (rRNA) molecules and proteins. In eukaryotic cells, the smaller subunit is denoted as the 40S subunit, while the larger subunit is referred to as the 60S subunit. In prokaryotic cells, these subunits are named the 30S and 50S subunits, respectively. The ribosome's overall structure resembles a "doughnut" or a "cotton reel," with grooves and binding sites for various factors involved in protein synthesis.
Ribosomes can be found floating freely within the cytoplasm of cells or attached to the endoplasmic reticulum (ER) membrane, forming part of the rough ER. Membrane-bound ribosomes are responsible for synthesizing proteins that will be transported across the ER and ultimately secreted from the cell or inserted into the membrane. In contrast, cytoplasmic ribosomes synthesize proteins destined for use within the cytoplasm or organelles.
In summary, ribosomes are essential components of cells that facilitate protein synthesis by translating mRNA into functional polypeptide chains. They can be found in various cellular locations and exist as either free-floating entities or membrane-bound structures.
Eukaryotic Initiation Factor-1 (eIF-1) is a protein involved in the initiation phase of protein synthesis in eukaryotic cells. It plays a crucial role in the assembly and recognition of the 40S ribosomal subunit, which is a key step in the formation of the initiation complex during translation.
eIF-1 helps to maintain the correct positioning of the initiator tRNA (tRNAi) at the P site of the small ribosomal subunit and prevents premature binding of the large ribosomal subunit. This ensures that protein synthesis begins at the correct start codon (AUG) in the mRNA.
In addition to its role in translation initiation, eIF-1 has also been implicated in other cellular processes such as DNA repair and apoptosis. Dysregulation of eIF-1 function has been linked to various diseases, including cancer and neurological disorders.
Molecular sequence data refers to the specific arrangement of molecules, most commonly nucleotides in DNA or RNA, or amino acids in proteins, that make up a biological macromolecule. This data is generated through laboratory techniques such as sequencing, and provides information about the exact order of the constituent molecules. This data is crucial in various fields of biology, including genetics, evolution, and molecular biology, allowing for comparisons between different organisms, identification of genetic variations, and studies of gene function and regulation.
Eukaryotic Initiation Factor-2B (eIF-2B) is a multi-subunit protein complex that plays a crucial role in the initiation phase of protein synthesis in eukaryotic cells. It is also known as the guanine nucleotide exchange factor for eIF-2 because its primary function is to catalyze the exchange of GDP (guanosine diphosphate) for GTP (guanosine triphosphate) on the alpha subunit of eukaryotic Initiation Factor-2 (eIF-2). This exchange is essential for the recycling of eIF-2, allowing it to participate in another round of initiation.
The eIF-2B complex consists of five subunits, denoted as p130, p125, p116, p100, and p65 (also known as eIF2B1, eIF2B2, eIF2B3, eIF2B4, and eIF2B5, respectively). The activity of eIF-2B is regulated by phosphorylation, particularly at the alpha subunit of eIF-2 (eIF2α), which can lead to an inhibition of its guanine nucleotide exchange factor activity. This phosphorylation event plays a critical role in the regulation of protein synthesis during cellular stress responses and is involved in various cellular processes, including growth, differentiation, and apoptosis.
Transfer RNA (tRNA) is a type of RNA molecule that plays a crucial role in protein synthesis, the process by which cells create proteins. During protein synthesis, tRNAs serve as adaptors, translating the genetic code present in messenger RNA (mRNA) into the corresponding amino acids required to build a protein.
Each tRNA molecule has an anticodon region that can base-pair with specific codons (three-nucleotide sequences) on the mRNA. At the other end of the tRNA is the acceptor stem, which contains a binding site for the corresponding amino acid. When an amino acid attaches to the tRNA, it forms an ester bond between the carboxyl group of the amino acid and the 3'-hydroxyl group of the ribose in the tRNA. This aminoacylated tRNA then participates in the translation process, delivering the amino acid to the growing polypeptide chain at the ribosome.
In summary, transfer RNA (tRNA) is a type of RNA molecule that facilitates protein synthesis by transporting and delivering specific amino acids to the ribosome for incorporation into a polypeptide chain, based on the codon-anticodon pairing between tRNAs and messenger RNA (mRNA).
Reticulocytes are immature red blood cells that still contain remnants of organelles, such as ribosomes and mitochondria, which are typically found in developing cells. These organelles are involved in the process of protein synthesis and energy production, respectively. Reticulocytes are released from the bone marrow into the bloodstream, where they continue to mature into fully developed red blood cells called erythrocytes.
Reticulocytes can be identified under a microscope by their staining characteristics, which reveal a network of fine filaments or granules known as the reticular apparatus. This apparatus is composed of residual ribosomal RNA and other proteins that have not yet been completely eliminated during the maturation process.
The percentage of reticulocytes in the blood can be used as a measure of bone marrow function and erythropoiesis, or red blood cell production. An increased reticulocyte count may indicate an appropriate response to blood loss, hemolysis, or other conditions that cause anemia, while a decreased count may suggest impaired bone marrow function or a deficiency in erythropoietin, the hormone responsible for stimulating red blood cell production.
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