Recombinant Saccharomyces cerevisiae Meiotic mRNA stability protein kinase SSN3 (SSN3), partial

Component of the SRB8-11 complex. The SRB8-11 complex is a regulatory module of the Mediator complex which is itself involved in regulation of basal and activated RNA polymerase II-dependent transcription. The SRB8-11 complex may be involved in the transcriptional repression of a subset of genes regulated by Mediator. It may inhibit the association of the Mediator complex with RNA polymerase II to form the holoenzyme complex. The SRB8-11 complex phosphorylates the C-terminal domain (CTD) of the largest subunit of RNA polymerase II RPB1 at serines 2 and 5. The SSN3/SRB10 and SSN8/SRB11 kinase-cyclin pair may also positively and negatively regulate numerous transcriptional activators in response to changes in nutritional and physiological conditions. Phosphorylates GCN4, promoting its ubiquitin-mediated degradation, and MSN2, promoting its nuclear exclusion. Phosphorylates STE12, thereby promoting its degradation and inhibition of filamentous growth. Phosphorylates GAL4, and this phosphorylation is required for efficient galactose-inducible transcription. Also phosphorylates BDF1 and the TAF2 subunit of the TFIID complex.