FISSION YEAST CDC24(+) ENCODES A NOVEL REPLICATION FACTOR REQUIRED FOR CHROMOSOME INTEGRITY

A mutation within the Schizoaccharomyces pombe cdc24(+) gene was ident ified previously in a screen for cell division cycle mutants and the c dc24(+) gene was determined to be essential for S phase in this yeast. We have isolated the cdc24(+) gene by complementation of a new temper ature-sensitive allele of the gene, cdc24-G1. The DNA sequence predict s the presence of an open reading frame punctuated by six introns whic h encodes a pioneer protein of 58 kD. A cdc24 null mutant was generate d by homologous recombination. Haploid cells lacking cdc24(+) are invi able, indicating that cdc24(+) is an essential gene. The transcript of cdc24(+) is present at constant levels throughout the cell cycle. Cel ls lacking cdc24(+) function show a checkpoint-dependent arrest with a 2N DNA content, indicating a block late in S phase. Arrest is accompa nied by a rapid loss of viability and chromosome breakage. An S. pombe homolog of the replicative DNA helicase DNA2 of S. cerevisiae suppres ses cdc24. These results suggest that Cdc24p plays a role in the progr ession of normal DNA replication and is required to maintain genomic i ntegrity.