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Regulatory protein GAL4 | |||||||
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Identifiers | |||||||
Organism | |||||||
Symbol | GAL4 | ||||||
Entrez | 855828 | ||||||
UniProt | P04386 | ||||||
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The Gal4 transcription factor is a positive regulator of gene expression of galactose-induced genes. [1] This protein represents a large fungal family of transcription factors, Gal4 family, which includes over 50 members in the yeast Saccharomyces cerevisiae e.g. Oaf1, Pip2, Pdr1, Pdr3, Leu3. [2]
Gal4 recognizes genes with UASG, an upstream activating sequence, and activates them. In yeast cells, the principal targets are GAL1 (galactokinase), GAL10 (UDP-glucose 4-epimerase), and GAL7 (galactose-1-phosphate uridylyltransferase), three enzymes required for galactose metabolism. This binding has also proven useful in constructing the GAL4/UAS system, a technique for controlling expression in insects. [3] In yeast, Gal4 is by default repressed by Gal80, and activated in the presence of galactose as Gal3 binds away Gal80. [4]
Two executive domains, DNA binding and activation domains, provide key function of the Gal4 protein conforming to most of the transcription factors.
Gal4 N-terminus is a zinc finger and belongs to the Zn(2)-C6 fungal family. It forms a Zn – cysteines thiolate cluster, [5] [6] and specifically recognizes UASG in GAL1 promoter. [7] [8]
Localised to the C-terminus, belongs to the nine amino acids transactivation domain family, 9aaTAD, together with Oaf1, Pip2, Pdr1, Pdr3, but also p53, E2A, MLL. [9] [10]
Galactose induces Gal4 mediated transcription albeit Glucose causes severe repression. [11] [12]
As a part of the Gal4 regulation, inhibitory protein Gal80 recognises and binds to the Gal4 region (853-874 aa). [13] [14] [15]
The inhibitory protein Gal80 is sequestered by regulatory protein Gal3 in Galactose dependent manner. This allows for Gal4 to work when there is galactose. [16] [4] [17] [18]
The Gal4 loss-of-function mutant gal4-64 (1-852 aa, deletion of the Gal4 C-terminal 29 aa) lost both interaction with Gal80 and activation function. [19] [20] [21]
In the Gal4 reverted mutant Gal4C-62 mutant, [22] a sequence (QTAY N AFMN) with the 9aaTAD pattern emerged and restored activation function of the Gal4 protein.
The activation domain Gal4 is inhibited by C-terminal domain in some Gal4 constructs. [23] [24]
The Gal4 activation function is mediated by MED15 (Gal11). [25] [26] [27] [28] [29] [30] [31]
The Gal4 protein interacts also with other mediators of transcription as are Tra1, [32] [33] [34] TAF9, [35] and SAGA/MED15 complex. [36] [37]
A subunit of the 26 S proteasome Sug2 regulatory protein has a molecular and functional interaction with Gal4 function. [38] [39] Proteolytic turnover of the Gal4 transcription factor is not required for function in vivo. [40] The native Gal4 monoubiquitination protects from 19S-mediated destabilizing under inducing conditions. [41]
The broad use of the Gal4 is in yeast two-hybrid screening to screen or to assay protein-protein interactions in eukaryotic cells from yeast to human.
In the GAL4/UAS system, the Gal4 protein and Gal4 upstream activating region (UAS) are used to study the gene expression and function in organisms such as the fruit fly. [3]
The Gal4 and inhibitory protein Gal80 have found application in a genetics technique for creating individually labeled homozygous cells called MARCM (Mosaic analysis with a repressible cell marker).
The MADS box is a conserved sequence motif. The genes which contain this motif are called the MADS-box gene family. The MADS box encodes the DNA-binding MADS domain. The MADS domain binds to DNA sequences of high similarity to the motif CC[A/T]6GG termed the CArG-box. MADS-domain proteins are generally transcription factors. The length of the MADS-box reported by various researchers varies somewhat, but typical lengths are in the range of 168 to 180 base pairs, i.e. the encoded MADS domain has a length of 56 to 60 amino acids. There is evidence that the MADS domain evolved from a sequence stretch of a type II topoisomerase in a common ancestor of all extant eukaryotes.
TEAD2, together with TEAD1, defines a novel family of transcription factors, the TEAD family, highly conserved through evolution. TEAD proteins were notably found in Drosophila (Scalloped), C. elegans, S. cerevisiae and A. nidulans. TEAD2 has been less studied than TEAD1 but a few studies revealed its role during development.
DNA-directed RNA polymerases I, II, and III subunit RPABC3 is a protein that in humans is encoded by the POLR2H gene.
DNA-directed RNA polymerases I, II, and III subunit RPABC5 is a protein that in humans is encoded by the POLR2L gene.
Histone deacetylase 4, also known as HDAC4, is a protein that in humans is encoded by the HDAC4 gene.
Myocyte-specific enhancer factor 2C also known as MADS box transcription enhancer factor 2, polypeptide C is a protein that in humans is encoded by the MEF2C gene. MEF2C is a transcription factor in the Mef2 family.
Probable global transcription activator SNF2L2 is a protein that in humans is encoded by the SMARCA2 gene.
Mediator of RNA polymerase II transcription subunit 15, also known as Gal11, Spt13 in yeast and PCQAP, ARC105, or TIG-1 in humans is a protein encoded by the MED15 gene.
G1/S-specific cyclin Cln3 is a protein that is encoded by the CLN3 gene. The Cln3 protein is a budding yeast G1 cyclin that controls the timing of Start, the point of commitment to a mitotic cell cycle. It is an upstream regulator of the other G1 cyclins, and it is thought to be the key regulator linking cell growth to cell cycle progression. It is a 65 kD, unstable protein; like other cyclins, it functions by binding and activating cyclin-dependent kinase (CDK).
Pho4 is a protein with a basic helix-loop-helix (bHLH) transcription factor. It is found in S. cerevisiae and other yeasts. It functions as a transcription factor to regulate phosphate responsive genes located in yeast cells. The Pho4 protein homodimer is able to do this by binding to DNA sequences containing the bHLH binding site 5'-CACGTG-3'. This sequence is found in the promoters of genes up-regulated in response to phosphate availability such as the PHO5 gene.
The meiotic recombination checkpoint monitors meiotic recombination during meiosis, and blocks the entry into metaphase I if recombination is not efficiently processed.
An upstream activating sequence or upstream activation sequence (UAS) is a cis-acting regulatory sequence. It is distinct from the promoter and increases the expression of a neighbouring gene. Due to its essential role in activating transcription, the upstream activating sequence is often considered to be analogous to the function of the enhancer in multicellular eukaryotes. Upstream activation sequences are a crucial part of induction, enhancing the expression of the protein of interest through increased transcriptional activity. The upstream activation sequence is found adjacently upstream to a minimal promoter and serves as a binding site for transactivators. If the transcriptional transactivator does not bind to the UAS in the proper orientation then transcription cannot begin. To further understand the function of an upstream activation sequence, it is beneficial to see its role in the cascade of events that lead to transcription activation. The pathway begins when activators bind to their target at the UAS recruiting a mediator. A TATA-binding protein subunit of a transcription factor then binds to the TATA box, recruiting additional transcription factors. The mediator then recruits RNA polymerase II to the pre-initiation complex. Once initiated, RNA polymerase II is released from the complex and transcription begins.
Cdc4 is a substrate recognition component of the SCF ubiquitin ligase complex, which acts as a mediator of ubiquitin transfer to target proteins, leading to their subsequent degradation via the ubiquitin-proteasome pathway. Cdc4 targets primarily cell cycle regulators for proteolysis. It serves the function of an adaptor that brings target molecules to the core SCF complex. Cdc4 was originally identified in the model organism Saccharomyces cerevisiae. CDC4 gene function is required at G1/S and G2/M transitions during mitosis and at various stages during meiosis.
Ira Herskowitz was an American phage and yeast geneticist who studied genetic regulatory circuits and mechanisms. He was particularly noted for his work on mating type switching and cellular differentiation, largely using Saccharomyces cerevisiae as a model organism.
Cryptic unstable transcripts (CUTs) are a subset of non-coding RNAs (ncRNAs) that are produced from intergenic and intragenic regions. CUTs were first observed in S. cerevisiae yeast models and are found in most eukaryotes. Some basic characteristics of CUTs include a length of around 200–800 base pairs, a 5' cap, poly-adenylated tail, and rapid degradation due to the combined activity of poly-adenylating polymerases and exosome complexes. CUT transcription occurs through RNA Polymerase II and initiates from nucleosome-depleted regions, often in an antisense orientation. To date, CUTs have a relatively uncharacterized function but have been implicated in a number of putative gene regulation and silencing pathways. Thousands of loci leading to the generation of CUTs have been described in the yeast genome. Additionally, stable uncharacterized transcripts, or SUTs, have also been detected in cells and bear many similarities to CUTs but are not degraded through the same pathways.
Ure2, or Ure2p, is a yeast protein encoded by a gene known as URE2. The Ure2 protein can also form a yeast prion known as [URE3]. When Ura2p is expressed at high levels in yeast, it will readily convert from its native protein conformation into an aggregate known as an amyloid. [URE3], along with [PSI+], were both determined by Wickner (1994) to meet the genetic definition of a yeast prion.
The transactivation domain or trans-activating domain (TAD) is a transcription factor scaffold domain which contains binding sites for other proteins such as transcription coregulators. These binding sites are frequently referred to as activation functions (AFs). TADs are named after their amino acid composition. These amino acids are either essential for the activity or simply the most abundant in the TAD. Transactivation by the Gal4 transcription factor is mediated by acidic amino acids, whereas hydrophobic residues in Gcn4 play a similar role. Hence, the TADs in Gal4 and Gcn4 are referred to as acidic or hydrophobic, respectively.
Pdr1p is a transcription factor found in yeast and is a key regulator of genes involved in general drug response. It induces the expression of ATP-binding cassette transporter, which can export toxic substances out of the cell, allowing cells to survive under general toxic chemicals. It binds to DNA sequences that contain certain motifs called pleiotropic drug response element (PDRE). Pdr1p is encoded by a gene called PDR1 on chromosome VII.
BCK2, also named CTR7, is an early cell cycle regulator expressed by the yeast Saccharomyces cerevisiae. It was first discovered in a screen for genes whose overexpression would suppress the phenotypes of PKC1 pathway mutations. Though its mechanism is currently unknown, it is believed to interact with Swi4 and Mcm1, both important transcriptional regulators of early cell cycle.
Kevin Struhl is an American molecular biologist and the David Wesley Gaiser Professor of Biological Chemistry and Molecular Pharmacology at Harvard Medical School. Struhl is primarily known for his work on transcriptional regulatory mechanisms in yeast using molecular, genetic, biochemical, and genomic approaches. More recently, he has used related approaches to study transcriptional regulatory circuits involved in cellular transformation and the formation of cancer stem cells.