Histone H3 K56 hyperacetylation perturbs replisomes and causes DNA damage

Deacetylation of histone H3 K56, regulated by the sirtuins Hst3p and Hst4p, is critical for maintenance of, genomic stability. However, the physiological consequences of a hick, of H3 K56 deacetylation m-c poorly understood. Here we show that cells lacking Hst3p) and Hst4p, in which H3 K56 is constitutively, hyperacetylated, exhibit hallmarks of spontaneous DNA damage, such is activation of the checkpoint kinase Rad53p and upregulation of DNA-damage inducible genes. Consistently, hst3 hst4 cells display synthetic lethality interactions with mutations that cripple genes involved in DNA replication and DNA double-strand break (DSB) repair. In most cases, synthetic lethality depends upon hyperacetylation of H3 K56 because it can he suppressed by mutation of K56 to arginine, which mimics the nonacetylated state. We also show that hst3 hst4 phenotypes can he suppressed by overexpression of the PCNA clamp loader large subunit, Rfclp, and by inactivation of, the alternative-clamp loaders CTF18, RAD24, and ELGI. Loss of, CTF4, encoding a replisome component involved in sister chromatid cohesion, also suppresses hst3 hst4 phenotypes. Genetic analysis suggests that CTF4 is a part of the K56 acetylation pathway that converges on and modulates replisomes function. This pahtway represents an important mechanism for maintenance of genomic stability mid depends upon proper regulation of H3 K56 acetylation by Hst3p and Hst4p. Our data also suggest the existence of a precarious balance between Rfclp and the other RFC complexes and that the nonreplicative forms of RFC are strongly deleterious to cells that have genomewide and constitutive H3 K56 hyperacetylation.