Rereplication phenomenon in fission yeast requires MCM proteins and other S phase genes

The fission yeast Schizosaccharomyces pombe can be induced to perform multi ple rounds of DNA replication without intervening mitoses by manipulating t he activity of the cyclin-dependent kinase p34(cdc2). We have examined the role in this abnormal rereplication of a large panel of genes known to be i nvolved in normal S phase. The genes analyzed can be grouped into four clas ses: (1) those that have no effect on rereplication, (2) others that delay DNA accumulation, (3) several that allow a gradual increase in DNA content but not in genome equivalents, and finally, (4) mutations that completely b lock rereplication. The rereplication induced by overexpression of the CDK inhibitor. Rum1p or depletion of the Cdc13p cyclin is essentially the same and requires the activity of two minor B-type cyclins, cig1(+) and cig2(+). In particular, the level, composition, and localization of the MCMI protei n complex does nor alter during rereplication. Thus rereplication in fissio n yeast mimics the DNA synthesis of normal S-phase, and the inability to re replicate provides an excellent assay for novel S-phase mutants.