An essential Saccharomyces cerevisiae single‐stranded DNA binding protein is homologous to the large subunit of human RP‐A

Single‐stranded DNA binding proteins (SSBs) are known to play a role in DNA replication and recombination in prokaryotes. An SSB was previously purified from the yeast Saccharomyces cerevisiae. This SSB stimulated the activity of a cognate strand exchange protein (SEP1) in vitro suggesting a role in recombination. We have cloned and functionally analyzed the gene encoding this protein. DNA sequencing of the cloned DNA revealed a 621 amino acid open reading frame with a coding potential for a Mr 70,269 polypeptide. Highly significant amino acid homology was detected between this S.cerevisiae gene and the Mr 70,000 subunit polypeptide of human RP‐A, a cellular protein essential for SV40 DNA replication in vitro. Therefore, we named the S.cerevisiae gene RPA1. RPA1 encodes an essential function in this organism as shown by tetrad analysis of heterozygous insertion mutants and is continuously required for mitotic growth. Cells lacking RPA1 accumulate as multiply budded cells with a single nucleus suggesting a defect in DNA replication.