PCT1(+), WHICH ENCODES A NEW DNA-BINDING PARTNER OF P85(CDC10), IS REQUIRED FOR MEIOSIS IN THE FISSION YEAST SCHIZOSACCHAROMYCES-POMBE

The transcriptional activation of genes at late G(1) is an important regulatory step in the commitment to a new cell division cycle. In Schizosaccharomyces pombe, this regulation is mediated by MCB elements that serve as binding sites for the MBF/DSC-1 complex. The cdc10(+)-encoded protein is a component of this complex. We report the cloning of a new gene, pct1(+), encoding a 73-kD protein that interacts with p85(cdc10) to form an MCB-binding heteromer. Pct1(+) is related to, but distinct from, the res1(+)/sct1(+) gene that also encodes a p85(cdc10) partner. p73(pct1) has centrally located ankyrin repeats and a putative amino-terminal DNA-binding domain that has extensive sequence similarity to the DNA-binding domains of the Saccharomyces cerevisiae SWI4 and MBP1 proteins. The p73(pct1)/p85(cdc10) complex binds both in vitro and in vivo to MCB but not SCB or E2F sites. Overexpression of pct1(+) is sufficient to rescue the growth of the cdc10-129 temperature-sensitive mutant at the restrictive temperature, although it is unable to rescue a cdc10 null mutation. A deletion of pct1(+) is not lethal but does result in a severe meiotic defect. Our results indicate that there are two cdc10-containing heteromeric complexes that bind to MCB elements and play differential roles in mitotic division and meiosis.