Requirement
of HSM3
for spontaneous mutagenesis in Saccharomyces cerevisiae
Vladimir Korolev,
Irina Fedorova, Svetlana Kovaltzova, Ludmila Gracheva, Tatiana Evstuhina
Laboratory of Eucaryote Genetics, Division of Molecular and Radiation
Biophysics, Petersburg Nuclear Physics Institute, RAS, 188350 Orlova Roscha,
Gatchina, Leningrad distr., Russia (lge@omrb.pnpi.spb.ru)
Early we showed that hsm3 mutation increased the level of spontaneous mutagenesis in slowly dividing cells, but this mutagenesis was not altered in rapidly growing hsm3 cells. The spontaneous mutagenesis consists from two components: mutations arise from replication errors and from spontaneous DNA damage repair errors. We checked influence hsm3 mutation on these components. We used mutants showing increased the replication error levels (pol3, pol2 and pms1 mutants) as well as mutants with decreased repair of spontaneous DNA damage (rad). Combinations of hsm3 mutation with each of the above mentioned mutations decreased the level of spontaneous mutation. The pol3-01 mutation is lethal in combination with null mutation in PMS1 cells; this lethality has been suggested to result from the accumulation of catastrophic levels of mutations in this strain. Triple mutant cells were viable and showed very high spontaneous mutation level. Thus, hsm3 mutation dramatically decreases the level of spontaneous mutation caused by replication errors and lack of their repair. To increase the level of spontaneous DNA damage we used the nucleotide excision repair mutants. The double mutants bearing any of NER-mutations and hsm3 deletion show significantly increased spontaneous mutation level in comparison with any single mutant. Thus, mutation hsm3 dramatically increases the spontaneous mutation rate caused by nonrepaired spontaneous DNA damage and this increase is dependent on REV3 function.