Suppressors of thermosensitive mutations in the DNA polymerase delta gene of Saccharomyces cerevisiae.

DNA polymerases (Pol) alpha, delta and epsilon are necessary for replication of nuclear DNA. Pol delta interacts permanently or transiently with numerous accessory proteins whose identification may shed light on the function(s) of Pol delta. In vitro mutagenesis was used to induce thermosensitive (ts) mutations in the DNA polymerase delta gene (POL3). We have attempted to clone two recessive extragenic suppressors of such ts mutants (sdp1 for mutation pol3-14 and sdp5-1 for mutation pol3-11) by transforming thermoresistant haploid strains pol3-14 sdp1 and pol3-11 sdp5-1 with wild-type genomic libraries in singlecopy or multicopy vectors. None of the thermosensitive transformants so obtained was identified as being sdp1 or sdp5-1. Instead, three genes were cloned whose products interfere with the activity of suppressors. One of them is the type 1 protein phosphatase gene, DIS2. Another is a novel gene, ASM4, whose gene product is rich in asparagine and glutamine residues.