FIGURE 1.

Mutation rates of wild type and mutant DNA Pol δ yeast. A, haploid yeast expressing mutant Pol δ were subjected to fluctuation analysis in the canavanine sulfate (CAN1) forward mutagenesis assay, and mutation rates were calculated using MSS maximum likelihood. The error bars indicate the 95% confidence interval. B, schematic representation of the region proximal to Ala⁶⁹⁹ (yellow) showing the P-helix (green) harboring motif B, and N-terminal domain helices (blue). The four putative interacting residues Met⁵⁴⁰, Tyr⁵³⁷, Asn⁵³⁶, and Glu⁴⁷¹ are represented as gray sticks. The incoming dCTP (silver) is shown interacting with Lys⁷⁰¹ and Asn⁷⁰⁵ of motif B and the template G (pink) and is provided for context. The image was produced in PyMOL using Protein Data Bank code 3IAY (The PyMOL Molecular Graphics System, version 1.2r3pre, Schrödinger, LLC.). C, mutation rates of single and double mutants at the CAN1 locus. The M540A substitution suppresses the mutator effect of A699Q. Tyr⁵³⁶ and Asn⁵³⁷ show evidence of interaction with A699Q (see “Results” and “Discussion”).