A novel role for Dun1 in the regulation of origin firing upon hyper-acetylation of H3K56

Abstract

During DNA replication newly synthesized histones are incorporated into the chromatin of the replicating sister chromatids. In the yeast Saccharomyces cerevisiae new histone H3 molecules are acetylated at lysine 56. This modification is carefully regulated during the cell cycle, and any disruption of this process is a source of genomic instability. Here we show that the protein kinase Dun1 is necessary in order to maintain viability in the absence of the histone deacetylases Hst3 and Hst4, which remove the acetyl moiety from histone H3. This lethality is not due to the well-characterized role of Dun1 in upregulating dNTPs, but rather because Dun1 is needed in order to counteract the checkpoint kinase Rad53 (human CHK2) that represses the activity of late firing origins. Deletion of CTF18, encoding the large subunit of an alternative RFC-like complex (RLC), but not of components of the Elg1 or Rad24 RLCs, is enough to overcome the dependency of cells with hyper-acetylated histones on Dun1. We show that the detrimental function of Ctf18 depends on its interaction with the leading strand polymerase, Polε. Our results thus show that the main problem of cells with hyper-acetylated histones is the regulation of their temporal and replication programs, and uncover novel functions for the Dun1 protein kinase and the Ctf18 clamp loader.

PCNA Loaders and Unloaders—One Ring That Rules Them All

“…Another striking role of Ctf18 is its phenotype in response to hyper-acetylation of histones [77]. Histone deposition on newly synthesized DNA is a complicated mechanism controlled and regulated by histone modification, mainly H3K56Ac in yeast cells [78,79].…”

“…Interestingly, deleting any RLCs major subunits on the background of hst3∆ hst4∆ suppresses the TS phenotype of this strain [82]. However, only deletion of CTF18 suppresses the lethality of dun1∆ in the hst3∆ hst4∆ background [77]. Dun1 is a protein kinase that acts in the DDR after being activated by phosphorylation by the checkpoint kinase Rad53.…”

The Amazing Acrobat: Yeast’s Histone H3K56 Juggles Several Important Roles While Maintaining Perfect Balance

“…Recently it was shown that hyper-acetylation of H3K56 affects the dynamics of the overall replication, by affecting firing of origins. In the presence of hyper-acetylation, there is constant activation of Rad53, which must be counteracted by the Dun1 checkpoint protein kinase for cells to survive [58]. The activation of Rad53 by the hyper-acetylated state of the chromatin (which is discussed extensively below in the context of checkpoint activation) causes Rad53 to inhibit late firing origins, and this in turn forces forks to traverse longer distances in order to complete genome duplication.…”

“…Rrm3 is a helicase that travels with the fork and is required for the replisome to pass through protein-DNA complexes [62]. Deletion of Rrm3 was found to suppress the TS phenotype of hst3 hst4 [58]. However, mutations in the acetylation machinery (Asf1, Rtt109, Rtt101, Mms1, and Mms22) together with deletion of Rrm3 are all lethal [63].…”

“…This over-abundance of firing leaves Mrc1 mutants with very few dormant origin reserves in case of fork stall and collapse. Cells deleted for Mrc1 are also synthetic lethal with hst3 hst4's replicative function [58]. These cells experience slow replication kinetics despite the over-abundance of firing, but are able to survive if factors, which limit replication elongation, such as Ctf18 and Rtt101, are deleted [69].…”