While the role of group I and group II intron-encoded proteins in homing has been well defined, the function of these proteins in intron dissemination to new sites remains the subject of intense study. These mobile introns, their intron-encoded proteins, and the mechanisms by which mobility occurs are the subject of this chapter. Although transition metals are not required for colicin DNase activity, it is likely that they play a stabilizing role related to the membrane translocation that must occur for colicins biological function. These data lend credence to the idea that the HNH domain, like the GIY-YIG domain, is an endonu clease cassette that can become associated with other protein domains to form multifunctional proteins. The open reading frames (ORFs) specifying group II intron-encoded proteins, when present, are located in the loop region of the structural domain IV, with most of the coding sequence outside the intron catalytic core. Of the three activities of the group II intron-encoded
Group II Self-Splicing Introns. -pre-rRNA of fungal and plant mitochondria -majority of chloroplast introns -several classes -require Mg 2+ -no cofactor. Domain Structure of a Group II Intron. A. 5 exon. 3 exon. Chemistry of Group II Self-Splicing. 1st step. 2nd step. lariat. Slideshow 3387240 by guang
Structure and Conformational Dynamics of the Domain 5 RNA Hairpin of a Bacterial Group II Intron Revealed by Solution Nuclear Magnetic Resonance and Molecular Dynamics ...
Exon shuffling was first introduced in 1978 when Walter Gilbert discovered that the existence of introns could play a major role in the evolution of proteins. It was noted that recombination within introns could help assort exons independently and that repetitive segments in the middle of introns could create hotspots for recombination to shuffle the exonic sequences. However, the presence of these introns in eukaryotes and absence in prokaryotes created a debate about the time in which these introns appeared. Two theories arose: the "introns early" theory and the "introns late" theory. Supporters of the "introns early theory" believed that introns and RNA splicing were the relics of the RNA world and therefore both prokaryotes and eukaryotes had introns in the beginning. However, prokaryotes eliminated their introns in order to obtain a higher efficiency, while eukaryotes retained the introns and the genetic plasticity of the ancestors. On the other hand, supporters of the "introns late" theory ...
about Alamut. "We are very pleased with Alamut since it conveniently streamlines post-sequencing analyses of detected variants. We value the programme user friendliness and its all-in one approach to variant analysis.". PROF. MILAN MACEK Jr. M.D. Ph.D ...
The objective of this study was primarily to determine the structure and biochemical characteristics of the NmeGp1Sd in order to gain a deeper insight into the evolution of metazoan Nme proteins and their functions.. Sponge Group I Nme genes are intron-rich and these introns are relatively short. The same has been found for introns in several other sponge genes [42, 43] and recently in A. queenslandica genome where median intron size is 80 bp [32]. The fourth intron (Figure 1) is likely the most ancient because it is also found in a choanoflagellate Group I Nme homolog. We conclude that the ancestral metazoan Group I Nme gene was intron-rich and probably had all four introns that are still present in most extant basal metazoan homologs. The ancestral gene structure is also well preserved in vertebrate homologs with three out of four introns present. D. melanogaster has only one of the ancestral introns and C. elegans lost all ancestral introns and gained two new ones which likely reflect ...
Introns may be lost or gained over evolutionary time, as shown by many comparative studies of orthologous genes. Subsequent analyses have identified thousands of examples of intron loss and gain events, and it has been proposed that the emergence of eukaryotes, or the initial stages of eukaryotic evolution, involved an intron invasion.[32] Two definitive mechanisms of intron loss, Reverse Transcriptase-Mediated Intron Loss (RTMIL) and genomic deletions, have been identified, and are known to occur.[33] The definitive mechanisms of intron gain, however, remain elusive and controversial. At least seven mechanisms of intron gain have been reported thus far: Intron Transposition, Transposon Insertion, Tandem Genomic Duplication, Intron Transfer, Intron Gain during Double-Strand Break Repair (DSBR), Insertion of a Group II Intron, and Intronization. In theory it should be easiest to deduce the origin of recently gained introns due to the lack of host-induced mutations, yet even introns gained ...
Many functional RNAs are required to fold into specific three-dimensional structures. A fundamental property of RNA is that its secondary structure and even some tertiary contacts are highly stable, which gives rise to independent modular RNA motifs and makes RNAs prone to adopting misfolded intermediates. Consequently, in addition to stabilizing the native structure relative to the unfolded species (defined here as stability), RNAs are faced with the challenge of stabilizing the native structure relative to alternative structures (defined as structural specificity). How RNAs have evolved to overcome these challenges is incompletely understood. Self-splicing group I introns have been used to study RNA structure and folding for decades. Among them, the Tetrahymena intron was the first discovered and has been studied extensively. In this work, we found that a version of the intron that was generated by in vitro selection for enhanced stability also displayed enhanced specificity against a stable ...
Group II introns are large metallo-ribozymes that use divalent metal ions in folding and catalysis. The 3-terminal domain 6 contains a conserved adenosine whose 2-OH acts as the nucleophile in the first splicing step. In the hierarchy of folding, D6 binds last into the active site. In order to investigate and understand the folding process to the catalytically active intron structure, it is important to know the individual binding affinities of Mg2+ ions to D6. We recently studied the solution structure of a 27 nucleotide long domain 6 (D6-27) from the mitochondrial yeast group II intron Sc.ai5, identifying also five Mg2+ binding sites including the one at the 5-terminal phosphate residues. Mg2+ coordination to the 5-terminal di- and triphosphate groups is strongest (e.g., log KA,TP = 4.55 ± 0.10) and could be evaluated here in detail for the first time. The other four binding sites within D6-27 are filled simultaneously (e.g., log KA,BR = 2.38 ± 0.06) and thus compete for the free Mg2+ ...
The exon/intron organisation of homologous nuclear genes was compared in several yeast species. CLUSTALX multiple alignments were performed to verify the degree of conservation of the homologues and to reconstruct a virtual (scaffold) gene, exhibiting the probable ancestral intron arrangement. Intron position was defined at the nucleotide level making it possible to determine whether the intron is at an identical position (same codon and same phase) or not in the homologues.. In the cases herein illustrated, some intron positions were found divergent in homologues sharing a high degree of sequence conservation, suggesting that these positions may result either from intron sliding or intron gain events [Bon et al., 2003]. Intron sliding is defined as the relocation of a pre-existing intron over short distances in the course of gene evolution [Rogozin et al., 2000, Trends Genet., 16, 430-432]. Although it is now admitted that intron sliding by one or two bases is a real phenomenon, it remains ...
This site contains information about the spliceosomal introns of the yeast Saccharomyces cerevisiae. Introns present special problems for the annotation of eukaryotic genomes. Splice sites are information-poor, and their recognition by the splicing apparatus is highly context-dependent and regulated, making identification by computational gene prediction programs a challenge. At present we do not understand splice site context well enough to predict which potential splice sites will be used, and thus how the genomic sequences will be expressed. Understanding the how and why of introns will require genome level information about splicing. One element of this will involve understanding splicing patterns and how they are regulated globally. Another element will involve understanding how splicing patterns change during evolution. To begin we study yeast, since it has the simplest known eukaryotic genome. In these pages we have listed known spliceosomal introns in the yeast genome and documented the ...
The wide, but scattered distribution of group I introns in nature is a result of two processes; the vertical inheritance of introns with or without losses, and the occasional transfer of introns across species barriers. Reversal of the group I intron
Most metazoan genes have multiple exons that must be carefully excised (from the pre-mRNA) and then ligated (to form the mRNA). This RNA splicing occurs in the nucleus, and upon its completion the mRNA is exported to the cytoplasm for translation. Exon definition complexes and spliceosomes begin to assemble during transcription. Some of these complexes interact with RNAP IIs CTD, and some introns are thus excised before transcription has even terminated.. There is no apparent order in which introns get spliced). Introns do no excise in any particular order, and active transcription (or its termination) is not needed for splicing to occur. However, the rate of transcription elongation through an intron can strongly affect what splice sites are chosen and thus indirectly couple transcription and splicing. Exon definition complexes and spliceosomes begin assembling during RNA synthesis; interaction with RNAP IIs CTD leads to excision of some introns before transcription has even ...
Isolation and Characterization of Functional Tripartite Group II Introns Using a Tn5-Based Genetic Screen. . Biblioteca virtual para leer y descargar libros, documentos, trabajos y tesis universitarias en PDF. Material universiario, documentación y tareas realizadas por universitarios en nuestra biblioteca. Para descargar gratis y para leer online.
... - reflects the multidimensional character of chemical biology, focusing in particular on the fundamental science of biological structures and systems, the use of chemical and biological techniques to elucidate
We read with great interest the recent paper by Beer and Sahin-Tóth1 addressing the missing heritability observed in approximately 60% of German cases of chronic pancreatitis.2 These authors opined that discovery studies tend to focus on exons and exon-intron boundaries and may thus miss many intronic variants.1 This premise seems eminently reasonable, given the generally much larger size of intronic sequences as compared with the coding sequences of protein-coding genes. However, there is a trade-off here. On the one hand, larger sequence size means larger target size for mutation, and hence the greater the number of mutations that could be missed if intronic sequences were not screened. On the other hand, to be of pathological significance, an intronic mutation must either create a new functional splicing donor or acceptor site or alternatively impact a functional sequence motif responsible for regulating splicing (eg, an intronic splicing enhancer), which depends upon many additional ...
There are many unanswered questions about introns. It is unclear whether introns serve some specific function, or whether they are selfish DNA which reproduces itself as a parasite.[5] Recent studies of entire eukaryotic genomes have now shown that the lengths and density (introns/gene) of introns varies considerably between related species. There are four or five different kinds of intron. Some introns represent mobile genetic elements (transposons). Alternative splicing of introns within a gene allows a variety of protein isoforms from a single gene. Thus multiple related proteins can be generated from a single gene and a single precursor mRNA transcript. The control of alternative RNA splicing is performed by complex network of signalling molecules. In humans, ~95% of genes with more than one exon are alternatively spliced.[6] ...
For each BAM, we use samtools to retrieve the reads in the region(s)) of interest. The reads are then filtered with samjs (https://github.com/lindenb/jvarkit/wiki/SamJS) to only keep the reads carrying an intron-exon junction at the desired location(s). Basically, the javascript-based filter loops over the CIGAR string of the read, computes the genomic interval skipped when the cigar operator is a deletion or a skipped region/intron. The read is printed if it describes the new intron-exon junction ...
We compared the expression patterns and functional annotations of genes with and without 5UIs. We found that the most highly expressed genes reveal a strong enrichment for having short 5UIs as opposed to having either no 5UIs or longer 5UIs. This effect was specific to genes with the highest expression levels and no relationship between length and expression level was observed for genes with intermediate or long introns (Figure2d). These results are contrary to the energetic cost model [23], which predicts that genes with no 5UIs will be more highly represented among those with the highest expression levels. Because expression reflects both production and degradation rates of mRNAs, our results suggest that short 5UIs tend to either enhance transcription or stabilize mature mRNAs.. The prevalence and the significance of these intron-dependent mechanisms of transcriptional enhancement at a genome-wide level are poorly understood in mammalian systems. There are a few examples in mammals of ...
An intron is any nucleotide sequence within a gene that is removed by RNA splicing to generate the final mature RNA product of a gene.[1][2]The term intron refers to both the DNA sequence within a gene, and the corresponding sequence in RNA transcripts.[3] Sequences that are joined together in the final mature RNA after RNA splicing are exons. Introns are found in the genes of most organisms and many viruses, and can be located in a wide range of genes, including those that generate proteins, ribosomal RNA (rRNA), and transfer RNA (tRNA). When proteins are generated from intron-containing genes, RNA splicing takes place as part of the RNA processing pathway that followstranscription and precedes translation ...
An intron is any nucleotide sequence within a gene that is removed by RNA splicing to generate the final mature RNA product of a gene.[1][2]The term intron refers to both the DNA sequence within a gene, and the corresponding sequence in RNA transcripts.[3] Sequences that are joined together in the final mature RNA after RNA splicing are exons. Introns are found in the genes of most organisms and many viruses, and can be located in a wide range of genes, including those that generate proteins, ribosomal RNA (rRNA), and transfer RNA (tRNA). When proteins are generated from intron-containing genes, RNA splicing takes place as part of the RNA processing pathway that followstranscription and precedes translation ...
[Ive combined all the previous intron entries together to make it easier to read. However, did not have the time to thoroughly edit, so some parts might seem a little repetitive.] Since I will be discussing introns, let me begin with a few points of clarification. First, I will be focusing on introns found in…
Comparison of gene expression from transgenes and endogenous genes with or without introns reveals a time-regulating role of introns in natural biological systems.
a Overview of MASP1 mutations. Exons and introns are indicated by circles with numbers and thin lines, respectively. The localization of mutations identified in
Then there are introns, which are often considered DNA spacers with a possible error-checking function, inside the DNA strand. Introns do not code for proteins. Some species have a lot of introns in total DNA. Exons are what is leftover in the DNA strand when the introns have been peeled off. Exons can be less than 60% of the total DNA. It is likely the introns are for a reason, but they do represent a change that is kind of like fiber filling, sort of a do-nothing or copy-proofing addition ...
Usually the primary challenge that follows the sequencing of anything from a small segment of DNA to a complete genome is to establish where the location functional elements such as: genes (intron/exon boundaries) promoters, terminators etc DNA sequences that may potentially encode proteins are called Open Reading Frames (ORFs) The situation in prokaryotes is relatively straightforward since scarcely any eubacterial and archaeal genes contain introns
Phylogenetic analysis of 71 group II intron ORFs. A maximum likelihood analysis of the amino acid sequence for 71 ORFs suggests the cox1 ORF718 of the marine ce
Lateral transfer of an intron to a homologous allele that lacks the intron, mediated by a site-specific endonuclease encoded within the mobile intron.
Berget, S.M., Sharp, P.A. (1977) A spliced sequence at the 5′-terminus of adenovirus late mRNA. Brookhaven Symp Biol, 29:332-44.. Berk, A.J., Sharp, P.A. (1977) Sizing and mapping of early adenovirus mRNAs by gel electrophoresis of S1 endonuclease-digested hybrids. Cell 12(3): 721-32.. Chow, L.T., Roberts, J.M., Lewis, J.B., Broker, T.R. (1977) A map of cytoplasmic RNA transcripts from lytic adenovirus type 2, determined by electron microscopy of RNA:DNA hybrids. Cell, 11(4): 819-36.. Gibbs, W.W. (2003) The unseen genome: gems among the junk. Scientific American 289(5):26-33.. Hooks, K. B., Delneri, D. & Grifths-Jones, S. (2014) Intron evolution in Saccharomycetaceae. Genome Biol. Evol. 6, 2543-2556.. Kabat, J.L., Barberan-Soler, S., McKenna, P., Clawson, H., Farrer, T., and Zahler, A.M. (2006) Intronic Alternative Splicing Regulators Identified by Comparative Genomics in Nematodes. PLoS Computational Biology 2(7):734-747.. Kiss, T. and Filipowicz, W. (1995) Genes and Development ...
Dear fly people: I have been trying to find some references about the cases in Drosophila in which one genes coding sequence (exon) resides in another genes intron region. I heard of examples, but would like to have a few papers to look at. Could someone give me a quick hand? Thanks a lot ...
All ESTs in GenBank on the date of the track data freeze for the given organism are used - none are discarded. When two ESTs have identical sequences, both are retained because this can be significant corroboration of a splice site.. ESTs are aligned against the genome using the Blat program. When a single EST aligns in multiple places, the alignment having the highest base identity is found. Only alignments that have a base identity level within a selected percentage of the best are kept. Alignments must also have a minimum base identity to be kept. For more information on the selection criteria specific to each organism, consult the description page accompanying the EST track for that organism.. The maximum intron length allowed by Blat is 500,000 bases, which may eliminate some ESTs with very long introns that might otherwise align. If an EST aligns non-contiguously (i.e. an intron has been spliced out), it is also a candidate for the Spliced EST track, provided it meets various quality ...
To test for conservation, researchers need to find matching stretches in the two species. This is relatively easy for stretches that "code" for proteins, where scientists long ago learned the meaning of the sequence. For "noncoding" regions, however, the comparison is often ambiguous. Even within a gene, stretches of DNA that code for pieces of the target protein are usually interspersed with much larger noncoding stretches, called introns, that are removed from the RNA working copy of the DNA before the protein is made.. Previously, researchers assumed that mutations in the middle of introns do not affect the final protein, so they simply accumulate. In the new study, however, the researchers found signs that evolution rejects some types of mutations even in these regions of the genome. Although the selection is weak, "introns are not neutral," in their effect on survival, says CSHLs Michael Zhang, who headed the research team.. To look for selection, co-researcher Chaolin Zhang looked in the ...
Gene can be much larger than unit that codes for protein(as u can conclude)Introns vary while exones are quite conserved(cause selection removes carriers of severe mutations in exones). Very long genes are the result of very long introns! In some techiniques you compare lengths of of alleles. That could be a sign of genetical relation. Could, but not definitely cause same lengh doesnt mean same nucleotide order. But if u compare more polymorphic regions and get covering in size between 2 individuals, the possibility that they are related is higher(again same size doesnt mean same nucleotide order ...
Supplementary Materials [Supplemental material] jbacter_187_15_5437__index. II introns are genetic retroelements capable of self-splicing and mobility that are common in prokaryotes. Originally discovered in organelles of Read More ...
A genomic DNA encoding an E8-like gene (CmE8, accession number AB071820) was isolated from melon and its nucleotide sequence was determined. The CmE8 consisted of three exons and two introns. The number and size of the exons and the location of introns were identical to those in tomato E8 gene. The deduced amino acid sequence of CmE8 consisted of 367 amino acids, and it was similar to those of 2-o ...
A catalogue of known hemiascomycetous yeast splicing signals was then used as bait to screen the batch of selected coding sequences, and to validate or not the presence of an intron ...
Intron je nukleotidna sekvenca unutar gena koja se uklanja putem RNK splajsovanja tokom formiranja finalnog RNK proizvoda.[1][2] Termin intron se odnosi na DNK sekvencu unutar gena, i odgovarajuću sekvencu RNK transkripta.[3] Sekvence koje se spajaju u finalnu maturiranu RNK nakon RNK splajsovanja su eksoni. Introni su prisutni u genima većine organizama i mnogim virusima. Oni se mogu naći u širokom nizu gena, uključujući one koji kodiraju proteine, ribozomsku RNK (rRNK), i transportnu RNK (tRNK). Tokom formirana proteina iz gena koji sadrže introne, dolazi do RNK splajsovanja nakon transkripcije i pre translacije. Reč intron je izvedena iz termina intrageni region, i.e. region unutar gena. ...
This track shows predictions from the Genscan program written by Chris Burge. The predictions are based on transcriptional, translational and donor/acceptor splicing signals as well as the length and compositional distributions of exons, introns and intergenic regions. For more information on the different gene tracks, see our Genes FAQ.. ...
This track shows predictions from the Genscan program written by Chris Burge. The predictions are based on transcriptional, translational and donor/acceptor splicing signals as well as the length and compositional distributions of exons, introns and intergenic regions. For more information on the different gene tracks, see our Genes FAQ.. ...
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Members of this protein family are multifunctional proteins encoded in most examples of bacterial group II introns. These group II introns are mobile selfish genetic elements, often with multiple highly identical copies per genome. Member proteins have an N-terminal reverse transcriptase (RNA-directed DNA polymerase) domain (PF00078) followed by an RNA-binding maturase domain (PF08388). Some members of this family may have an additional C-terminal DNA endonuclease domain that this model does not cover. A region of the group II intron ribozyme structure should be detectable nearby on the genome by Rfam model RF00029 ...
Although large scale informatics studies on introns can be useful in making broad inferences concerning patterns of intron gain and loss, more specific questions about intron evolution at a finer scale can be addressed using a gene family where structure and function are well known. Genome wide surveys of tetraspanins from a broad array of organisms with fully sequenced genomes are an excellent means to understand specifics of intron evolution. Our approach incorporated several new fully sequenced genomes that cover the major lineages of the animal kingdom as well as plants, protists and fungi. The analysis of exon/intron gene structure in such an evolutionary broad set of genomes allowed us to identify ancestral intron structure in tetraspanins throughout the eukaryotic tree of life. We performed a phylogenomic analysis of the intron/exon structure of the tetraspanin protein family. In addition, to the already characterized tetraspanin introns numbered 1 through 6 found in animals, three ...
Two types of spliceosomes catalyze splicing of pre-mRNAs. The major U2-type spliceosome is found in all eukaryotes and removes U2-type introns, which represent more than 99% of pre-mRNA introns. The minor U12-type spliceosome is found in some eukaryotes and removes U12-type introns, which are rare and have distinct splice consensus signals. The U12-type spliceosome consists of several small nuclear RNAs and associated proteins. This gene encodes a 65K protein that is a component of the U12-type spliceosome. This protein contains two RNA recognition motifs (RRMs), suggesting that it may contact one of the small nuclear RNAs of the minor spliceosome. [provided by RefSeq, Jul 2008 ...
The fission yeast genome, which contains numerous short introns, is an apt model for studies on fungal splicing mechanisms and splicing by intron definition. Here we perform a domain analysis of the evolutionarily conserved Schizosaccharomyces pombe pre-mRNA-processing factor, SpPrp18. Our mutational and biophysical analyses of the C-terminal alpha-helical bundle reveal critical roles for the conserved region as well as helix five. We generate a novel conditional missense mutant, spprp18-5. To assess the role of SpPrp18, we performed global splicing analyses on cells depleted of prp18(+) and the conditional spprp18-5 mutant, which show widespread but intron-specific defects. In the absence of functional SpPrp18, primer extension analyses on a tfIId(+) intron 1-containing minitranscript show accumulated pre-mRNA, whereas the lariat intron-exon 2 splicing intermediate was undetectable. These phenotypes also occurred in cells lacking both SpPrp18 and SpDbr1 (lariat debranching enzyme), a genetic ...
BackgroundThe genome of the pico-eukaryotic (bacterial-sized) prasinophyte green alga Ostreococcus lucimarinus has one of the highest gene densities known in eukaryotes, yet it contains many introns. Phylogenetic studies suggest this unusually compact genome (13.2 Mb) is an evolutionarily derived state among prasinophytes. The presence of introns in the highly reduced O. lucimarinus genome appears to be in opposition to simple explanations of genome evolution based on unidirectional tendencies, either neutral or selective. Therefore, patterns of intron retention in this species can potentially provide insights into the forces governing intron evolution.Methodology/Principal FindingsHere we studied intron features and levels of expression in O. lucimarinus using expressed sequence tags (ESTs) to annotate the current genome assembly. ESTs were assembled into unigene clusters that were mapped back to the O. lucimarinus Build 2.0 assembly using BLAST and the level of gene expression was inferred from the
DNA is made up of different units called nucleotides. There are a variety of four different nucleotides that make up the polymer that is DNA[1]. DNA consists of two different regions, one being exons and the other introns. The regions of exons in the DNA consist of fewer nucleotides than the regions of introns and are the regions that code for proteins[2]. It is also now thought that enhancer sequences for regulation of gene transcription is not just found in introns but also exons.[3]. Exons are the coding regions of a gene and are separated by regions of introns; they are copied during transcription (along with introns) to produce pre-mRNA[4] ...
TY - JOUR. T1 - Tissue-specific splicing regulator Fox-1 induces exon skipping by interfering E complex formation on the downstream intron of human F1γ gene. AU - Fukumura, Kazuhiro. AU - Kato, Ayako. AU - Jin, Yui. AU - Ideue, Takashi. AU - Hirose, Tetsuro. AU - Kataoka, Naoyuki. AU - Fujiwara, Toshinobu. AU - Sakamoto, Hiroshi. AU - Inoue, Kunio. PY - 2007/8/1. Y1 - 2007/8/1. N2 - Fox-1 is a regulator of tissue-specific splicing, via binding to the element (U)GCAUG in mRNA precursors, in muscles and neuronal cells. Fox-1 can regulate splicing positively or negatively, most likely depending on where it binds relative to the regulated exon. In cases where the (U)GCAUG element lies in an intron upstream of the alternative exon, Fox-1 protein functions as a splicing repressor to induce exon skipping. Here we report the mechanism of exon skipping regulated by Fox-1, using the hF1γ gene as a model system. We found that Fox-1 induces exon 9 skipping by repressing splicing of the downstream intron 9 ...
The classification of human gene sequences into exons and introns is a difficult problem in DNA sequence analysis. In this paper, we define a set of features, called the simple Z (SZ) features, which is derived from the Z-curve features for the recognition of human exons and introns. The classification results show that SZ features, while fewer in numbers ~three in total!, can preserve the high recognition rate of the original nine Z-curve features. Since the size of SZ features is one-third of the Z-curve features, the dimensionality of the feature space is much smaller, and better recognition efficiency is achieved. If the stop codon feature is used together with the three SZ features, a recognition rate of up to 92% for short sequences of length ,140 bp can be obtained ...
In contrast to bacteria which have no introns, eukaryotes (cells with a nucleus) have introns which are intervening sequences within genes which get spliced out when genes are transcribed and are not expressed in the protein. In contrast, exons are the sequences within a gene which do get expressed and translated into protein. Intergenic DNA, as the name suggests, is DNA between genes which does not code for proteins. Hope this helps gabriel vargas md/phd References Genes VII by Benjamin Lewin ...
This is a pretty good article on the origin of the spliceosome from self-splicing introns: Vosseberg J, Snel B. Domestication of self-splicing introns during eukaryogenesis: the rise of the complex spliceosomal machinery. Biol Direct. 2017 Dec 1;12(1):30. DOI:10.1186/s13062-017-0201-6 There are many interesting references given in that article also, for example on spliceosomal diversity. There are simple protozoan parasites known with as few as 27 introns in their entire genomes, and highly s...