Cdm1, the smallest subunit of DNA polymerase δ in the fission yeast Schizosaccharomyces pombe, is non-essential for growth and division

Highly purified DNA polymerase delta from the fission yeast Schizosaccharomyces pombe is a complex of at least four distinct subunits. Genes encoding three of these (pol3(+)/cdc6(+), cdc1(+) and cdc27(+)) have been characterised previously. Here we describe the isolation and characterisation of cdm1(+), the gene encoding the smallest (22 kDa) subunit of the Pol delta complex. Over-expression of cdm1(+), which encodes a 160 amino-acid protein with no significant sequence similarity to proteins in current databases, is able to rescue cells carrying temperature-sensitive mutations in either pol3(+)/cdc6(+), cdc1(+) or cdc27(+). Cells deleted for cdm1(+) are viable, indicating that cdm1(+) is non-essential for mitotic growth, and are no more sensitive to a variety of DNA replication inhibitors and DNA damaging agents than are wild-type cells. In addition, overexpression of cdm1(+) suppresses the temperature-sensitive cdc24-M38 mutant suggesting that cdc24(+) may also have a role in DNA polymerase delta function.