A role for Lsmlp in response to ultraviolet-radiation damage in Saccharomyces cerevisiae

A genome-wide screen in Saccharomyces cerevisiae identified LSM1 as a new gene affecting sensitivity to ultraviolet (UV) radiation. Lsmlp is a member of a cytoplasmic complex composed of Lsmlp-7p that interacts with the yeast mRNA degradation machinery. To investigate the potential role of Lsmlp in response to UV radiation, we constructed double mutant strains in which LSM1 was deleted in combination with a representative gene from each of three known yeast DNA repair pathways. Our results show that lsm1delta increases the UV-radiation sensitivity of the rad1delta and rad51delta mutants, but not the radl8delta mutant, placing LSM1 within the post-replication repair/damage tolerance pathway (PRR). When combined with other deletions affecting PRR, lsm1delta increases the UV-radiation sensitivity of the rev3delta, rad30delta and pol30-K164R mutants but not rad5delta. Furthermore, the UV-radiation sensitivity phenotype of lsmldelta is partially rescued by mutations in genes involved in 3' to 5' mRNA degradation, and mutations predicted to function in RNA interactions confer the most UV-radiation sensitivity. Together, these results suggest that Lsmlp may confer protection against UV-radiation damage by protecting the 3' ends of mRNAs from exosome-dependent 3' to 5' degradation as part of a novel RAD5-mediated, PCNA-K164 ubiquitylation-independent subpathway of PRR.