SAGA is important for prompt export of stress-inducible transcripts through Sgf73p-mediated mechanism

Previous studies suggested that stress-inducible genes are SAGA (Spt-Ada-Gcn5 acetyltransferase)-dominated and characterized by distinct chromatin structures on promoter regions; however, a detailed regulatory mechanism and evolutional advantage of such specialization are not fully understood yet. Here, we newly defined SAGA-regulated genes under direct control of Sgf73p of the deubiquitylating module (DUBm). Through genetic and biochemical analyses, we observed a functional relationship between Sgf73p and the essential mRNA export factor Yra1p; Sgf73p is critical for proper chromatin localization and RNA-binding of Yra1p. Additionally, under physiological condition, Sgf73p plays a central role in quality control of messenger ribonucleoparticles (mRNPs) biogenesis and export in conjunction with the nuclear exosome. Upon environmental stress, when immediate transport of specific transcripts is imperative, Sgf73p facilitates bypass of canonical surveillance and promotes timely export of necessary transcripts. Overall, our results show Sgf73p-mediated gene expression plasticity is important for cell tolerance to stress and thus survival amidst of the uncertain environment. ChIP-seq samples of Flag-tagged SAGA subunits (including Sgf73p and Sgf11p), Sua7p, Yra1p, and Rpb3p in wildtype and various mutants were prepared using budding yeast; ChIP-seq samples of Flag-tagged Sgf73p in wildtype, rpt2-1 and spt20del before and after heat shock (at 42degrees for 20min).