Characterization of Schizosaccharomyces pombe mcm7(+) and cdc23(+) (MCM10)and interactions with replication checkpoints

MCM proteins are required for the proper regulation of DNA replication. We cloned fission yeast mcm(7+) and showed it is essential for viability; spor es lacking mcm(7+) begin S phase later than wild-type cells and arrest with an apparent 2C DNA content. We isolated a novel temperature-sensitive alle le, mcm7-98, and also characterized two temperature-sensitive alleles of th e fission yeast homolog of MCM10, cdc23(+). mcm7-98 and both cdc23ts allele s arrest with damaged chromosomes and air S phase delay. We find that mcm7- 98 is synthetically lethal with the other mcmts mutants but does not intera ct genetically with either cdc23ts allele. However, cdc23-M36 interacts wit h mcm4ts. Unlike other mcm mutants or cdc23, mcm 7-98 is synthetically leth al with checkpoint mutants Delta cds1, Delta chk1, or Delta rad3, suggestin g chromosomal defects even at permissive temperature. Mcm7p is a nuclear pr otein throughout the cell cycle, and its localization is dependent on the o ther MCM proteins. Our data suggest that the Mcm3p-Mcm5p dimer interacts wi th the Mcm4p-Mcm6p-Mcm7p core. complex through Mcm7p.