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

The fission yeast Schizosaccharomyces pombe can be induced to perform multiple rounds of DNA replication without intervening mitoses by manipulating the 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 involved in normal S phase. The genes analyzed can be grouped into four classes: (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 block 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 MCM protein complex does not alter during rereplication. Thus rereplication in fission yeast mimics the DNA synthesis of normal S phase, and the inability to rereplicate provides an excellent assay for novel S-phase mutants.