RES2(+), A NEW MEMBER OF THE CDC10(+)/SWI4 FAMILY, CONTROLS THE START OF MITOTIC AND MEIOTIC CYCLES IN FISSION YEAST

In the fission yeast Schizosaccharomyces pombe, the cdc10(+) and res1(+) genes play a crucial role in the start of mitotic and meiotic cycles. They encode structurally related transcriptional complex proteins and regulate some S phase-specific genes. Here we report the identification of a new member of this family named as res2(+). res2(+) has been isolated as a multicopy suppressor of a res1(-) null mutant and specifies a 73 kDa protein, which has two copies of the Swi/ankyrin moth and shares the highest sequence and structure similarity with the Res1 protein. res2(+) is largely redundant in function with res1(+) and is required for the initiation of mitotic and premeiotic DNA synthesis, but has an additional role in meiotic division. Unlike res1(+), res2(+) is highly induced during conjugation and strongly depends on cdc10(+) for its activity. We conclude that the fission yeast contains two functionally overlapping parallel 'start' systems, Res1-Cdc10 and Res2-Cdc10, the former of which plays a major role in mitotic cycle whereas the latter in meiotic cycle.