Английская Википедия:Gal4 transcription factor
Шаблон:Multiple issues Шаблон:Infobox nonhuman protein
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 UASШаблон:Sub, 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]
Domains
Two executive domains, DNA binding and activation domains, provide key function of the Gal4 protein conforming to most of the transcription factors.
DNA binding
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 UASШаблон:Sub in GAL1 promoter. [7][8]
Gal4 transactivation
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]
Regulation
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]
Mutants
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.
Inactive constructs
The activation domain Gal4 is inhibited by C-terminal domain in some Gal4 constructs.[23][24]
Function
Target
Transcription
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]
Proteosome
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]
Application
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).
See also
References
Further reading
- Gal4p on WikiGenes
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