Mutator suppression and escape from replication error-induced extinction in yeast.
Cells rely on a network of conserved pathways to govern DNA replication fidelity. Loss of polymerase proofreading or mismatch repair elevates spontaneous mutation and facilitates cellular adaptation. However, double mutants are inviable, suggesting that extreme mutation rates exceed an error threshold. Here we combine alleles that affect DNA polymerase δ (Pol δ) proofreading and mismatch repair to define the maximal error rate in haploid yeast and to characterize genetic suppressors of mutator phenotypes. We show that populations tolerate mutation rates 1,000-fold above wild-type levels but collapse when the rate exceeds 10⁻³ inactivating mutations per gene per cell division. Variants that escape this error-induced extinction (eex) rapidly emerge from mutator clones. One-third of the escape mutants result from second-site changes in Pol δ that suppress the proofreading-deficient phenotype, while two-thirds are extragenic. The structural locations of the Pol δ changes suggest multiple antimutator mechanisms. Our studies reveal the transient nature of eukaryotic mutators and show that mutator phenotypes are readily suppressed by genetic adaptation. This has implications for the role of mutator phenotypes in cancer.
Department of Pathology, University of Washington, Seattle, Washington, United States of America.
Alan J
AJ
Herr
Masanori
M
Ogawa
Nicole A
NA
Lawrence
Lindsey N
LN
Williams
Julie M
JM
Eggington
Mallika
M
Singh
Robert A
RA
Smith
Bradley D
BD
Preston
D000483:Alleles; D000818:Animals; D004249:DNA Damage / Q000235:genetics; D004258:DNA Polymerase III / Q000235:genetics / Q000378:metabolism*; D004260:DNA Repair / Q000235:genetics; D004261:DNA Replication / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics; D005838:Genotype; D006238:Haploidy; D051379:Mice; D053842:Microsatellite Instability; D059645:Mutation Rate; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D013489:Suppression, Genetic / Q000235:genetics*
C491232:POL3 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D004258:DNA Polymerase III