Role of Histone H3 Lysine 56 Acetylation in the Response to Replicative stress
In Saccharomyces cerevisiae, histone H3 lysine 56 acetylation (H3K56ac) occurs on all newly synthesized histones H3 that are deposited behind DNA replication forks. H3K56ac plays critical role in chromatin assembly during DNA replication and repair. H3K56ac is also required for genome stability and stabilization of stalled replication fork. Cells lacking H3K56ac are sensitive to methyl methane sulfonate and other drugs that cause replicative stress.  In this thesis, we investigated the links between the replisome protein Ctf4 and the H3K56 acetyltransferase Rtt109. Deletion of CTF4 partially rescued the sensitivity of rtt109Δ cells to methyl methane sulfonate. Genetic analyses also showed that Ctf4, Rtt109, and the Rtt101-Mms1-Mms22 complex act in the same pathway to response to replicative stress. ctf4Δ and rtt109Δ cells displayed intense foci of the single-stranded DNA binding complex RPA during replicative stress, suggesting formation of excess single-stranded DNA regions at stalled replication forks, leading to hyper activation of DNA damage checkpoints. These mutants accumulated anaphase bridges and persistent foci of the homologous recombination proteins Rad51 and Rad52 in response to genotoxins, suggesting that abnormal DNA structure formed at stalled replisome may compromise their recovery. Deletion of HR genes (RAD51, RAD52, RAD54, RAD55 and MUS81) together with ctf4Δ and rtt109Δ presents synergistic sensitivity to MMS, suggesting that H3K56ac deficient cells use HR to repair the damages caused by replicative stress. Overall our results demonstrate that H3K56ac deficient cells cannot recover MMS- induced damages because HR is compromised in these mutants.
Ctf4 Rtt109 MMS Histone H3 Lysine 56 acetylation Chromatin structure Post-translational histone modifications DNA replication DNA replication coupled chromatin assembly DNA damage response pathway Homologous recombination