Gal4 transcription factor
The Gal4 transcription factor is a positive regulator of gene expression of galactose-induced genes.
The Gal4 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.
Two executive domains, DNA binding and activation domains, provide key function of the Gal4 protein conforming to the most of transcription factors.
Localised to the N-terminus, belongs to the Zn(2)-C6 fungal family, which forms a Zn – cysteines thiolate cluster.
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.
Galactose induces Gal4 mediated transcription albeit Glucose causes severe repression.
As a part of the Gal4 regulation, inhibitory protein Gal80 recognises and binds to the Gal4 region (853-874 aa) encompassing the Gal4 activation domain 9aaTAD.
The inhibitory protein Gal80 is sequestered by regulatory protein Gal3 in Galactose dependent manner.
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.
In the Gal4 reverted mutant Gal4C-62 mutant, a sequence (QTAY N AFMN) with the 9aaTAD pattern emerged and restored activation function of the Gal4 protein.(doi: https://doi.org/10.1101/110882)
The activation domain Gal4 is inhibited by C-terminal domain in some Gal4 constructs. (doi: https://doi.org/10.1101/110882)
A subunit of the 26 S proteasome Sug2 regulatory protein has a molecular and functional interaction with Gal4 function.
Proteolytic turnover of the Gal4 transcription factor is not required for function in vivo.
The native Gal4 monoubiquitination protects from 19S-mediated destabilizing under inducing conditions.
The Gal4 activation function is mediated by MED15 (Gal11).
The Gal4 protein interacts also with other mediators of transcription as are Tra1,TAF9, and SAGA/MED15 complex. (http://mcb.asm.org/content/25/1/114/F8.large.jpg)
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