Abstract
Asf1 is a conserved histone H3/H4 chaperone. We find that Asf1 in budding yeast promotes an essential cellular response to replication stress caused by the ribonucleotide reductase inhibitor hydroxyurea. That is, Asf1 stimulates derepression of DNA damage response (DDR) genes during the S phase. Derepression of DDR genes strongly correlates with Asf1 binding to their promoters. Having identified the C terminus and histone-binding domains of Asf1 as molecular determinants of its constitutive and inducible association with chromatin, we tested whether Asf1 binding to DDR genes is mechanistically important for their derepression. Our results provide little support for this hypothesis. Rather, the contribution of Asf1 to DDR gene derepression depends on its ability to stimulate H3K56 acetylation by lysine acetyltransferase Rtt109. The precise regulation of H3K56 acetylation in the promoters of DDR genes is unexpected: DDR gene promoters are occupied by H3K56-acetylated nucleosomes under repressing conditions, and the steady state level of H3K56 promoter acetylation does not change upon derepression. We propose that replication-coupled deposition of Lys56-acetylated H3 poises the DDR genes in newly synthesized daughter duplexes for derepression during the S phase. In this model, the presence of a histone mark that destabilizes nucleosomes is compatible with suppression of transcription because in the uninduced state, DDR gene promoters are constitutively occupied by a potent repressor-corepressor complex.
Highlights
Asf1 is a conserved histone H3/H4 chaperone
Full Derepression of a DNA Damage Response Gene by Replication Stress Signals Requires Asf1—Microarrray and Northern blotting experiments revealed abnormally high expression of a subset of DNA damage response (DDR) genes in asf1⌬ cells grown under normal conditions (Fig. 1A and supplemental Fig. S1)
In further investigating the mechanism used by Asf1 to promote DDR gene transcription in response to replication stress, we considered the recent evidence from the Tyler lab that H3K56 acetylation is important for the induction of PHO5 upon phosphate limitation [10]
Summary
Asf1 is a conserved histone H3/H4 chaperone. We find that Asf1 in budding yeast promotes an essential cellular response to replication stress caused by the ribonucleotide reductase inhibitor hydroxyurea. Consistent with the idea that Asf1 is present at the promoters of DDR genes to directly reconfigure nucleosomes, crosslinking of Asf1 to the promoters of RNR3 and HUG1 was readily detected by ChIP in wild type cells grown under normal conditions (Fig. 2A shows the raw data from a representative experiment).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
