Final Report Summary - COACTIVATOR (Regulation of gene expression by transcriptional coactivators)
Our second objective is to address how chromatin regulatory complexes are assembled and whether their assembly can be modulated to control their activities, focusing on the highly conserved SAGA co-activator. Its largest subunit, Tra1, is required for recruiting SAGA to promoters. Tra1 is a member of the PIKK family of kinases, but lacks catalytic residues. Recent work has established that PIKKs are activated by a novel chaperone, TTT. We accumulated biochemical and functional evidence that Tra1, although a pseudo-kinase, is assembled into SAGA by TTT. We identified key residues within SAGA and Tra1 that mediate their interaction and the domain of Tra1 which is recognized by TTT for its folding. Interestingly, this domain is conserved between all PIKKs, suggesting a shared molecular mechanism of assembly. Finally, we showed that TTT recognizes nascent, unfolded PIKKs, to catalyze their folding and incorporation into active complexes.
In conclusion, our work has uncovered a previously unknown mechanism for the regulation of transcription by signaling pathways and strengthen an emerging concept in the field of signal transduction and gene regulation, which is that specific chaperones control the assembly of multi-protein complexes to coordinate their activities.