Cooperation between the INO80 Complex and Histone Chaperones Determines Adaptation of Stress Gene Transcription in the Yeast Saccharomyces cerevisiae

Abstract

In yeast, environmental stresses provoke sudden and dramatic increases in gene expression at stress-inducible loci. Stress gene transcription is accompanied by the transient eviction of histones from the promoter and the transcribed regions of these genes. We found that mutants defective in subunits of the INO80 complex, as well as in several histone chaperone systems, exhibit extended expression windows that can be correlated with a distinct delay in histone redeposition during adaptation. Surprisingly, Ino80 became associated with the ORFs of stress genes in a stress-specific way, suggesting a direct function in the repression during adaptation. This recruitment required elongation by RNA polymerase (Pol) II but none of the histone modifications that are usually associated with active transcription, such as H3 K4/K36 methylation. A mutant lacking the Asf1-associated H3K56 acetyltransferase Rtt109 or Asf1 itself also showed enhanced stress-induced transcript levels. Genetic data, however, suggest that Asf1 and Rtt109 function in parallel with INO80 to restore histone homeostasis, whereas Spt6 seems to have a function that overlaps that of the chromatin remodeler. Thus, chromatin remodeling by INO80 in cooperation with Spt6 determines the shape of the expression profile under acute stress conditions, possibly by an elongation-dependent mechanism.