Gal4 transcription factor

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Structures	Swiss-model
Domains	InterPro

Regulatory protein GAL4
Identifiers
Organism	Saccharomyces cerevisiae
Symbol	GAL4
Entrez	855828
UniProt	P04386
Search for
Structures	Swiss-model
Domains	InterPro
	Wikidata Q27549381

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 UAS_G, 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.

Gal4 domains and regulation

DNA binding

Gal4 N-terminus is a zinc finger of the belongs to the Zn(2)-C6 fungal family. It forms a Zn – cysteines thiolate cluster,[5][6] and specifically recognizes UAS_G 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][32]

The Gal4 protein interacts also with other mediators of transcription as are Tra1,[33][34][35][36][37] TAF9,[38] and SAGA/MED15 complex.[39][40]

Proteosome

A subunit of the 26 S proteasome Sug2 regulatory protein has a molecular and functional interaction with Gal4 function.[41][42] Proteolytic turnover of the Gal4 transcription factor is not required for function in vivo.[43] The native Gal4 monoubiquitination protects from 19S-mediated destabilizing under inducing conditions.[44]

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).

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