Mechanisms of surveillance of DNA replication and DNA repair are essential for genome stability and cell viability. Both the integrity of the repair pathways and the timely regulation of the repair mechanisms are essential for the maintenance of genome stability. One of the layers of regulation of DNA repair is the control of protein abundance, both at a global cellular level, and locally at the site of damage. This is achieved through transcriptional regulation of protein synthesis and through the control of protein stability and turnover. In this study, we investigate the role of Rad56 and Cmr1 in yeast Saccharomyces cerevisiae, two novel players in the maintenance of genome integrity, which act through modulation of turnover or stability of repair and replication proteins.
In S. cerevisiae, RAD56 belongs to the RAD52 epistasis group of genetic loci that confer X-ray but not UV sensitivity when mutant. Prior to the work presented here, all these loci have been mapped to a specific gene except RAD56. We map the rad56-1 mutation to the NAT3 gene, which encodes the catalytic subunit of the NatB N-terminal acetyltransferase in yeast. Deletion of RAD56 causes sensitivity to X-rays, methyl methanesulfonate, zeocin, camptothecin and hydroxyurea, but not to UV light, suggesting that N-terminal acetylation of specific DNA repair proteins is important for efficient DNA repair.
Cmr1 is a poorly characterized protein, which localizes primarily to the nucleus. The protein has appeared in several large-scale studies investigating factors involved in DNA metabolism, but no specific function has been assigned to Cmr1. Taking advantage of a series of high-throughput screens we characterize Cmr1 as a chromatinassociated protein, involved in the regulation of fork progression in the presence of replication stress. Moreover, we dissect the association of Cmr1 and other nuclear and cytoplasmic proteins to the JUNQ compartment in response to replication stress, and propose a model where relocalization of replication-associated factors to the nuclear periphery is important for promoting fork stability and recovery after replication stress.