NuA4 Subunit Yng2 Function in Intra-S-Phase DNA Damage Response

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Abstract
While regulated transcription requires acetylation of histone N-terminal tails to promote an open chromatin conformation, a similar role for histone acetylation in DNA replication and/or repair remains to be established. Cells lacking the NuA4 subunit Yng2 are viable but critically deficient for genome-wide nucleosomal histone H4 acetylation. We found that yng2 mutants are specifically sensitized to DNA damage in S phase induced by cdc8 or cdc9 mutations, hydroxyurea, camptothecin, or methylmethane sulfonate (MMS). In yng2, MMS treatment causes a persistent Mec1-dependent intra-S-phase checkpoint delay characterized by slow DNA repair. Restoring H4 acetylation with the histone deacetylase inhibitor trichostatin A promotes checkpoint recovery. In turn, mutants lacking the histone H3-specific acetyltransferase GCN5 are similarly sensitive to intra-S-phase DNA damage. The inviability of gcn5 yng2 double mutants suggests overlapping roles for H3 and H4 acetylation in DNA replication and repair. Paradoxically, haploid yng2 mutants do not tolerate mutations in genes important for nonhomologous end joining repair yet remain proficient for homologous recombination. Our results implicate nucleosomal histone acetylation in maintaining genomic integrity during chromosomal replication.