PROLIFERATING CELL NUCLEAR ANTIGEN (POL30) MUTATIONS SUPPRESS CDC44 MUTATIONS AND IDENTIFY POTENTIAL REGIONS OF INTERACTION BETWEEN THE 2 ENCODED PROTEINS

In addition to its role as a processivity factor in DNA replication, p roliferating cell nuclear antigen (PCNA) may function in the regulatio n of cell cycle progression. We present genetic evidence that PCNA int eracts; with the gene product of CDC44, an essential nucleotide-bindin g protein that encodes the large subunit of yeast replication factor C (K. Fien and B. Stillman, personal communication). Mutations in POL30 (PCNA) suppress cold-sensitive alleles of cdc44 that contain mutation s in or near nucleotide-binding consensus domains, but they do not sup press a null allele. Thus, it appears that PCNA interacts with Cdc44p but cannot substitute for its function. pol30 mutations suppress addit ional phenotypes of cdc44 mutations, including the cold sensitivity th at they were selected to suppress. This observation suggests an intima te association between PCNA and Cdc44p. Each of five independent pol30 mutants contains a unique single mutation that maps to a localized re gion on one face of the predicted three-dimensional structure of PCNA. This face identifies a region likely to be important for functional i nteraction between the CDC44 and POL30 gene products.