Cyclin H is a type of protein that is classified as a cyclin, which is a regulatory subunit of cyclin-dependent kinases (CDKs). Specifically, Cyclin H forms a complex with CDK7 and functions as an essential component of the cell cycle transcriptional coactivator known as TFIIH.

TFIIH plays a crucial role in the initiation of transcription by RNA polymerase II and also participates in the process of DNA repair. The Cyclin H-CDK7 complex phosphorylates the carboxy-terminal domain (CTD) of the largest subunit of RNA polymerase II, which is a critical step in the transcription cycle. Additionally, Cyclin H-CDK7 also plays a role in regulating the cell cycle by controlling the activity of certain cell cycle regulators, such as E2F transcription factors.

Mutations in the gene that encodes Cyclin H have been associated with certain human diseases, including a rare inherited disorder called Cockayne syndrome, which is characterized by developmental abnormalities, neurological dysfunction, and premature aging.

Cyclin D1 is a type of cyclin protein that plays a crucial role in the regulation of the cell cycle, which is the process by which cells divide and grow. Specifically, Cyclin D1 is involved in the transition from the G1 phase to the S phase of the cell cycle. It does this by forming a complex with and acting as a regulatory subunit of cyclin-dependent kinase 4 (CDK4) or CDK6, which phosphorylates and inactivates the retinoblastoma protein (pRb). This allows the E2F transcription factors to be released and activate the transcription of genes required for DNA replication and cell cycle progression.

Overexpression of Cyclin D1 has been implicated in the development of various types of cancer, as it can lead to uncontrolled cell growth and division. Therefore, Cyclin D1 is an important target for cancer therapy, and inhibitors of CDK4/6 have been developed to treat certain types of cancer that overexpress Cyclin D1.

Cyclin A is a type of cyclin protein that regulates the progression of the cell cycle, particularly through the G1 and S phases. It forms a complex with and acts as a regulatory subunit for cyclin-dependent kinases (CDKs), specifically CDK2 and CDK1. The activation of Cyclin A-CDK complexes leads to phosphorylation of various target proteins, which in turn regulates DNA replication and the transition to mitosis.

Cyclin A levels rise during the late G1 phase and peak during the S phase, after which they decline rapidly during the G2 phase. Any abnormalities in Cyclin A regulation or expression can contribute to uncontrolled cell growth and cancer development.

Cyclin-dependent kinases (CDKs) are a family of serine/threonine protein kinases that play crucial roles in regulating the cell cycle, transcription, and other cellular processes. They are activated by binding to cyclin proteins, which accumulate and degrade at specific stages of the cell cycle. The activation of CDKs leads to phosphorylation of various downstream target proteins, resulting in the promotion or inhibition of different cell cycle events. Dysregulation of CDKs has been implicated in several human diseases, including cancer, and they are considered important targets for drug development.

Cyclin E is a type of cyclin protein that plays a crucial role in the regulation of the cell cycle, particularly during the G1 phase and the transition to the S phase. It functions as a regulatory subunit of the Cyclin-dependent kinase 2 (CDK2) complex, which is responsible for promoting the progression of the cell cycle.

Cyclin E is synthesized during the late G1 phase of the cell cycle and accumulates to high levels until it forms a complex with CDK2. The Cyclin E-CDK2 complex then phosphorylates several target proteins, leading to the activation of various downstream pathways that promote DNA replication and cell cycle progression.

The regulation of Cyclin E expression and activity is tightly controlled through multiple mechanisms, including transcriptional regulation, protein stability, and proteasomal degradation. Dysregulation of Cyclin E has been implicated in various human cancers, including breast, ovarian, and lung cancer, due to its role in promoting uncontrolled cell proliferation and genomic instability.

Cyclins are a family of regulatory proteins that play a crucial role in the cell cycle, which is the series of events that take place as a cell grows, divides, and produces two daughter cells. They are called cyclins because their levels fluctuate or cycle during the different stages of the cell cycle.

Cyclins function as subunits of serine/threonine protein kinase complexes, forming an active enzyme that adds phosphate groups to other proteins, thereby modifying their activity. This post-translational modification is a critical mechanism for controlling various cellular processes, including the regulation of the cell cycle.

There are several types of cyclins (A, B, D, and E), each of which is active during specific phases of the cell cycle:

1. Cyclin D: Expressed in the G1 phase, it helps to initiate the cell cycle by activating cyclin-dependent kinases (CDKs) that promote progression through the G1 restriction point.
2. Cyclin E: Active during late G1 and early S phases, it forms a complex with CDK2 to regulate the transition from G1 to S phase, where DNA replication occurs.
3. Cyclin A: Expressed in the S and G2 phases, it associates with both CDK2 and CDK1 to control the progression through the S and G2 phases and entry into mitosis (M phase).
4. Cyclin B: Active during late G2 and M phases, it partners with CDK1 to regulate the onset of mitosis by controlling the breakdown of the nuclear envelope, chromosome condensation, and spindle formation.

The activity of cyclins is tightly controlled through several mechanisms, including transcriptional regulation, protein degradation, and phosphorylation/dephosphorylation events. Dysregulation of cyclin expression or function can lead to uncontrolled cell growth and proliferation, which are hallmarks of cancer.

Cyclin B is a type of cyclin protein that regulates the cell cycle, specifically the transition from G2 phase to mitosis (M phase) in eukaryotic cells. Cyclin B binds and activates cyclin-dependent kinase 1 (CDK1), forming the complex known as M-phase promoting factor (MPF). This complex triggers the events leading to cell division, such as chromosome condensation, nuclear envelope breakdown, and spindle formation. The levels of cyclin B increase during the G2 phase and are degraded by the anaphase-promoting complex/cyclosome (APC/C) at the onset of anaphase, allowing the cell cycle to progress into the next phase.

Cyclin B1 is a type of cyclin protein that regulates the cell cycle, specifically the transition from G2 phase to mitosis (M phase) in eukaryotic cells. It forms a complex with and acts as a regulatory subunit of cyclin-dependent kinase 1 (CDK1), also known as CDC2. During the G2 phase, Cyclin B1 levels accumulate and upon reaching a certain threshold, it binds to CDK1 to form the maturation promoting factor (MPF). The activation of MPF triggers the onset of mitosis by promoting nuclear envelope breakdown, chromosome condensation, and other events required for cell division. After the completion of mitosis, Cyclin B1 is degraded by the ubiquitin-proteasome system, allowing the cell cycle to progress back into G1 phase.

Cyclin D2 is a type of cyclin protein that regulates the cell cycle, particularly in the G1 phase. It forms a complex with and acts as a regulatory subunit of cyclin-dependent kinase 4 (CDK4) or CDK6, promoting the transition from G1 to S phase of the cell cycle. The expression of cyclin D2 is regulated by various growth factors, hormones, and oncogenes, and its dysregulation has been implicated in the development of several types of cancer.

Cyclin D3 is a type of cyclin protein that regulates the cell cycle, particularly during the G1 phase. It forms a complex with and acts as a regulatory subunit of CDK4 or CDK6, which are cyclin-dependent kinases. This complex plays a crucial role in phosphorylating and inactivating the retinoblastoma protein (pRb), leading to the release of E2F transcription factors that promote the expression of genes required for DNA replication and cell cycle progression into the S phase.

Cyclin D3 is primarily expressed in activated lymphocytes and is essential for normal immune function, as well as in certain tissues during development. Alterations in CYCLIN D3 gene expression or function have been implicated in several types of cancer, such as leukemias and lymphomas, due to their role in uncontrolled cell proliferation.

Cyclin A1 is a type of cyclin protein that regulates the cell cycle, particularly during the S and G2 phases. It forms a complex with and acts as a regulatory subunit of cyclin-dependent kinase 2 (CDK2), helping to control the transition from the G1 phase to the S phase and from the S phase to the G2 phase. Cyclin A1 is expressed in various tissues, including ovary, testis, bone marrow, and lymphoid cells. Overexpression or dysregulation of cyclin A1 has been implicated in several types of cancer, making it a potential target for cancer therapy.

Cyclin A2 is a type of cyclin protein that regulates the cell cycle, which is the series of events that cells undergo as they grow and divide. Specifically, Cyclin A2 plays a role in the progression from the G1 phase to the S phase (DNA synthesis phase) and from the G2 phase to the M phase (mitosis phase) of the cell cycle. It does this by binding to and activating cyclin-dependent kinases (CDKs), which are enzymes that help regulate the cell cycle.

Cyclin A2 is expressed at various points during the cell cycle, but its levels peak during the S and G2 phases. The protein is degraded during mitosis, ensuring that it is not present in excess during the next cell cycle. Dysregulation of Cyclin A2 has been implicated in the development of cancer, as uncontrolled cell growth and division are hallmarks of this disease.

Cyclin D is a type of cyclin protein that plays a crucial role in the regulation of the cell cycle, which is the process by which cells grow and divide. Specifically, Cyclin D is involved in the G1 phase of the cell cycle and works in conjunction with its partner enzyme, cyclin-dependent kinase 4 (CDK4) or CDK6, to phosphorylate and regulate the activity of several key proteins that control the transition from G1 to S phase.

There are several different types of Cyclin D proteins, including Cyclin D1, Cyclin D2, and Cyclin D3, which are encoded by different genes but share similar structures and functions. Overexpression or dysregulation of Cyclin D has been implicated in the development of various human cancers, as it can lead to uncontrolled cell growth and division. Therefore, understanding the role of Cyclin D in the cell cycle and its regulation is important for developing potential cancer therapies.

Transcription Factor IIH (TFIIH) is a multi-subunit protein complex that plays a crucial role in the process of transcription, which is the synthesis of RNA from DNA. Specifically, TFIIH is involved in the initiation phase of transcription for protein-coding genes in eukaryotic cells.

TFIIH has two main enzymatic activities: helicase and kinase. The helicase activity is provided by the XPB and XPD subunits, which are responsible for unwinding the DNA double helix at the transcription start site. This creates a single-stranded DNA template for the RNA polymerase II (Pol II) enzyme to bind and begin transcribing the gene.

The kinase activity of TFIIH is provided by the CAK subcomplex, which consists of the CDK7, Cyclin H, and MAT1 proteins. This kinase phosphorylates the carboxy-terminal domain (CTD) of the largest subunit of Pol II, leading to the recruitment of additional transcription factors and the initiation of RNA synthesis.

In addition to its role in transcription, TFIIH is also involved in DNA repair processes, particularly nucleotide excision repair (NER). During NER, TFIIH helps to recognize and remove damaged DNA lesions, such as those caused by UV radiation or chemical mutagens. The XPB and XPD subunits of TFIIH are essential for this process, as they help to unwind the DNA around the damage site and create a bubble structure that allows other repair factors to access and fix the lesion.

Mutations in the genes encoding various subunits of TFIIH can lead to several human diseases, including xeroderma pigmentosum (XP), Cockayne syndrome (CS), trichothiodystrophy (TTD), and combined XP/CS/TTD. These disorders are characterized by increased sensitivity to UV radiation, developmental abnormalities, and neurological dysfunction.

A blastula is a stage in the early development of many animals, including mammals. It is a hollow ball of cells that forms as a result of cleavage, which is the process of cell division during embryonic development. The blastula is typically characterized by the presence of a fluid-filled cavity called the blastocoel, which is surrounded by a single layer of cells known as the blastoderm.

In mammals, the blastula stage follows the morula stage, which is a solid mass of cells that results from cleavage of the fertilized egg. During further cell division and rearrangement, the cells in the morula become organized into an inner cell mass and an outer layer of cells, called the trophoblast. The inner cell mass will eventually give rise to the embryo proper, while the trophoblast will contribute to the formation of the placenta.

As the morula continues to divide and expand, it forms a cavity within the inner cell mass, which becomes the blastocoel. The single layer of cells surrounding the blastocoel is called the blastoderm. At this stage, the blastula is capable of further development through a process called gastrulation, during which the three germ layers of the embryo (ectoderm, mesoderm, and endoderm) are formed.

It's important to note that not all animals go through a blastula stage in their development. Some animals, such as insects and nematodes, have different patterns of early development that do not include a blastula stage.

Cyclin-Dependent Kinase 2 (CDK2) is a type of enzyme that plays a crucial role in the regulation of the cell cycle, which is the process by which cells grow and divide. CDK2 is activated when it binds to a regulatory subunit called a cyclin.

During the cell cycle, CDK2 helps to control the progression from the G1 phase to the S phase, where DNA replication occurs. Specifically, CDK2 phosphorylates various target proteins that are involved in the regulation of DNA replication and the initiation of mitosis, which is the process of cell division.

CDK2 activity is tightly regulated through a variety of mechanisms, including phosphorylation, dephosphorylation, and protein degradation. Dysregulation of CDK2 activity has been implicated in various human diseases, including cancer. Therefore, CDK2 is an important target for the development of therapies aimed at treating these diseases.

CDC2 and CDC28 are members of the Serine/Threonine protein kinase family, which play crucial roles in the regulation of the cell cycle. These kinases were originally identified in yeast (CDC28) and humans (CDC2), but they are highly conserved across eukaryotes.

CDC2-CDC28 Kinases function as a part of larger complexes, often associated with cyclins, to control different phases of the cell cycle by phosphorylating specific substrates at key regulatory points. The activity of CDC2-CDC28 Kinases is tightly regulated through various mechanisms, including phosphorylation, dephosphorylation, and protein binding interactions.

During the G2 phase of the cell cycle, CDC2-CDC28 Kinases are inactivated by phosphorylation at specific residues (Tyr15 and Thr14). As the cell approaches mitosis, a family of phosphatases called Cdc25 removes these inhibitory phosphates, leading to activation of the kinase. Activated CDC2-CDC28 Kinases then initiate mitotic processes such as chromosome condensation and nuclear envelope breakdown.

In summary, CDC2-CDC28 Kinases are essential regulators of the eukaryotic cell cycle, controlling various aspects of cell division through phosphorylation of specific substrates. Their activity is tightly regulated to ensure proper progression through the cell cycle and prevent uncontrolled cell growth, which can lead to diseases such as cancer.

Cyclin G1 is a type of protein that belongs to the cyclin family, which are involved in the regulation of the cell cycle. The cell cycle is the series of events that take place as a cell grows, copies its DNA, and divides into two daughter cells.

Cyclin G1 regulates the cell cycle by interacting with various cyclin-dependent kinases (CDKs), which are enzymes that help control the progression of the cell cycle. Specifically, Cyclin G1 has been shown to inhibit the activity of CDK1 and CDK2, which play important roles in regulating the transition from the G1 phase to the S phase of the cell cycle.

Cyclin G1 has also been implicated in other cellular processes, including DNA damage repair, apoptosis (programmed cell death), and tumor suppression. Dysregulation of Cyclin G1 has been linked to various types of cancer, making it a potential target for cancer therapy.

Cyclin G is a type of protein that belongs to the cyclin family, which are involved in the regulation of the cell cycle. The human Cyclin G gene encodes two isoforms, Cyclin G1 and Cyclin G2, which share a similar structure but have different functions.

Cyclin G1 is known to play a role in the negative regulation of the cell cycle, particularly during the G1 phase. It interacts with several proteins, including CDKs (cyclin-dependent kinases), to regulate the activity of various transcription factors and other signaling pathways that control cell growth and division.

Cyclin G2, on the other hand, has been implicated in the regulation of DNA damage response and apoptosis (programmed cell death). It interacts with CDKs and other proteins to modulate the activity of various signaling pathways involved in these processes.

Overall, Cyclin G plays important roles in regulating cell cycle progression, DNA damage response, and apoptosis, and its dysregulation has been linked to several human diseases, including cancer.

Protein-Serine-Threonine Kinases (PSTKs) are a type of protein kinase that catalyzes the transfer of a phosphate group from ATP to the hydroxyl side chains of serine or threonine residues on target proteins. This phosphorylation process plays a crucial role in various cellular signaling pathways, including regulation of metabolism, gene expression, cell cycle progression, and apoptosis. PSTKs are involved in many physiological and pathological processes, and their dysregulation has been implicated in several diseases, such as cancer, diabetes, and neurodegenerative disorders.

The cell cycle is a series of events that take place in a cell leading to its division and duplication. It consists of four main phases: G1 phase, S phase, G2 phase, and M phase.

During the G1 phase, the cell grows in size and synthesizes mRNA and proteins in preparation for DNA replication. In the S phase, the cell's DNA is copied, resulting in two complete sets of chromosomes. During the G2 phase, the cell continues to grow and produces more proteins and organelles necessary for cell division.

The M phase is the final stage of the cell cycle and consists of mitosis (nuclear division) and cytokinesis (cytoplasmic division). Mitosis results in two genetically identical daughter nuclei, while cytokinesis divides the cytoplasm and creates two separate daughter cells.

The cell cycle is regulated by various checkpoints that ensure the proper completion of each phase before progressing to the next. These checkpoints help prevent errors in DNA replication and division, which can lead to mutations and cancer.

Cyclin C is a type of cyclin protein that plays a crucial role in the regulation of the cell cycle, which is the process by which cells grow and divide. Specifically, Cyclin C is involved in the transition from the G1 phase to the S phase of the cell cycle, during which DNA replication occurs.

Cyclin C forms a complex with cyclin-dependent kinase 8 (CDK8) and other regulatory subunits to form the CDK8 module, which is part of the mediator complex that regulates gene transcription. The activity of Cyclin C/CDK8 is regulated by various mechanisms, including phosphorylation and degradation, to ensure proper control of the cell cycle and prevent uncontrolled cell growth and division.

Mutations in the gene encoding Cyclin C have been associated with certain types of cancer, highlighting its importance in maintaining genomic stability and preventing tumorigenesis.

Transcription factors (TFs) are proteins that regulate the transcription of genetic information from DNA to RNA by binding to specific DNA sequences. They play a crucial role in controlling gene expression, which is the process by which information in genes is converted into a functional product, such as a protein.

TFII, on the other hand, refers to a general class of transcription factors that are involved in the initiation of RNA polymerase II-dependent transcription. These proteins are often referred to as "general transcription factors" because they are required for the transcription of most protein-coding genes in eukaryotic cells.

TFII factors help to assemble the preinitiation complex (PIC) at the promoter region of a gene, which is a group of proteins that includes RNA polymerase II and other cofactors necessary for transcription. Once the PIC is assembled, TFII factors help to recruit RNA polymerase II to the promoter and initiate transcription.

Some examples of TFII factors include TFIIA, TFIIB, TFIID, TFIIE, TFIIF, and TFIIH. Each of these factors plays a specific role in the initiation of transcription, such as recognizing and binding to specific DNA sequences or modifying the chromatin structure around the promoter to make it more accessible to RNA polymerase II.

Cyclin B2 is a type of cyclin protein that regulates the cell cycle, particularly at the G2 phase and the beginning of mitosis. It forms a complex with and acts as a regulatory subunit of cyclin-dependent kinase 1 (CDK1), which plays a crucial role in the transition from G2 phase to mitosis. The expression and activity of Cyclin B2 are tightly regulated during the cell cycle, and its dysregulation can lead to abnormal cell division and contribute to the development of cancer.

Cyclin T is a type of cyclin protein that is encoded by the CCNT2 gene in humans. Cyclins are a family of regulatory proteins that play a crucial role in the cell cycle, which is the series of events that cells undergo as they grow and divide. Specifically, cyclin T is a component of the CDK9/cyclin T complex, also known as positive transcription elongation factor b (P-TEFb), which plays a key role in regulating gene expression by controlling the elongation phase of RNA polymerase II-mediated transcription.

Cyclin T is expressed at various stages of the cell cycle and has been shown to interact with several other proteins involved in cell cycle regulation, including the retinoblastoma protein (pRb) and the E2F family of transcription factors. Dysregulation of cyclin T expression or activity has been implicated in several human diseases, including cancer.

Phosphorylation is the process of adding a phosphate group (a molecule consisting of one phosphorus atom and four oxygen atoms) to a protein or other organic molecule, which is usually done by enzymes called kinases. This post-translational modification can change the function, localization, or activity of the target molecule, playing a crucial role in various cellular processes such as signal transduction, metabolism, and regulation of gene expression. Phosphorylation is reversible, and the removal of the phosphate group is facilitated by enzymes called phosphatases.

Neutral amino acid transport systems refer to a group of membrane transporters that facilitate the movement of neutral amino acids across cell membranes. Neutral amino acids are those that have a neutral charge at physiological pH and include amino acids such as alanine, serine, threonine, valine, leucine, isoleucine, methionine, cysteine, tyrosine, phenylalanine, and tryptophan.

There are several different transport systems that have been identified for neutral amino acids, each with its own specificity and affinity for different amino acids. Some of the major neutral amino acid transport systems include:

1. System A: This transporter preferentially transports small, neutral amino acids such as alanine, serine, and threonine. It is found in many tissues, including the intestines, kidneys, and brain.
2. System B0+: This transporter preferentially transports large, neutral amino acids such as leucine, isoleucine, valine, methionine, and phenylalanine. It is found in many tissues, including the intestines, kidneys, and brain.
3. System L: This transporter preferentially transports large, neutral amino acids such as leucine, isoleucine, valine, methionine, and phenylalanine. It is found in many tissues, including the intestines, kidneys, and brain.
4. System y+: This transporter preferentially transports cationic amino acids such as lysine and arginine, but it can also transport some neutral amino acids. It is found in many tissues, including the intestines, kidneys, and brain.
5. System b0,+: This transporter preferentially transports cationic amino acids such as lysine and arginine, but it can also transport some neutral amino acids. It is found in many tissues, including the intestines, kidneys, and brain.

These transport systems play important roles in maintaining amino acid homeostasis in the body, as well as in various physiological processes such as protein synthesis, neurotransmitter synthesis, and cell signaling. Dysregulation of these transport systems has been implicated in several diseases, including cancer, neurological disorders, and metabolic disorders.

Cyclin G2 is a type of protein that belongs to the cyclin family, which are involved in the regulation of the cell cycle. The cell cycle is the series of events that cells undergo as they grow and divide. Specifically, Cyclin G2 regulates the G1 phase of the cell cycle, which is the phase where the cell prepares to divide.

Cyclin G2 has been found to play a role in several important cellular processes, including DNA damage response, apoptosis (programmed cell death), and differentiation. It has also been implicated in the development of certain diseases, such as cancer. For example, Cyclin G2 has been shown to have tumor-suppressive functions, and its expression is often reduced in cancer cells.

In summary, Cyclin G2 is a regulatory protein that plays a critical role in controlling the cell cycle and maintaining genomic stability. Its dysregulation has been associated with various diseases, including cancer.

A holozyme is not a specific medical term, but rather a term used in biochemistry to refer to the complete, active form of an enzyme. An enzyme is a biological molecule that catalyzes chemical reactions in the body, and it is often made up of several different subunits or components.

The term "holozyme" comes from the Greek words "holos," meaning whole, and "enzyma," meaning in yeast. It was originally used to describe the active form of enzymes found in yeast cells, but it is now used more broadly to refer to any complete, active enzyme complex.

A holozyme typically consists of two types of subunits: a catalytic subunit, which contains the active site where the substrate binds and the reaction takes place, and one or more regulatory subunits, which control the activity of the enzyme under different conditions. The regulatory subunits may be activated or inhibited by various signals, such as hormones, metabolites, or other molecules, allowing the enzyme to respond to changes in the cellular environment.

In summary, a holozyme is the fully assembled and functional form of an enzyme, consisting of one or more catalytic subunits and one or more regulatory subunits that work together to carry out specific biochemical reactions in the body.

Cyclin-Dependent Kinase 4 (CDK4) is a type of enzyme, specifically a serine/threonine protein kinase, that plays a crucial role in the regulation of the cell cycle. The cell cycle is the series of events that take place in a cell leading to its division and duplication. CDK4, when activated by binding to cyclin D, helps to promote the transition from the G1 phase to the S phase of the cell cycle. This transition is a critical point in the regulation of cell growth and division, and dysregulation of this process can lead to uncontrolled cell growth and cancer. CDK4 inhibitors are used in the treatment of certain types of cancer, such as breast and lung cancer, to block the activity of CDK4 and prevent tumor cell proliferation.

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.

An encyclopedia is a comprehensive reference work containing articles on various topics, usually arranged in alphabetical order. In the context of medicine, a medical encyclopedia is a collection of articles that provide information about a wide range of medical topics, including diseases and conditions, treatments, tests, procedures, and anatomy and physiology. Medical encyclopedias may be published in print or electronic formats and are often used as a starting point for researching medical topics. They can provide reliable and accurate information on medical subjects, making them useful resources for healthcare professionals, students, and patients alike. Some well-known examples of medical encyclopedias include the Merck Manual and the Stedman's Medical Dictionary.

Maturation-Promoting Factor (MPF) is not a medical term per se, but it is commonly used in the field of cell biology and cancer research. MPF refers to a complex of two proteins that play a crucial role in regulating the cell cycle, specifically during the transition from the G2 phase to mitosis (M phase).

MPF is composed of a cyclin-dependent kinase (CDK1) and a regulatory subunit called cyclin B. During the late G2 phase, the levels of cyclin B increase, which leads to the activation of CDK1. Once activated, MPF triggers a series of events that promote mitosis, including chromosome condensation, nuclear envelope breakdown, and spindle formation.

In summary, Maturation-Promoting Factor (MPF) is a protein complex made up of CDK1 and cyclin B, which regulates the transition from the G2 phase to mitosis during the cell cycle.