Multiple mutations are common at mouse Aprt in genotoxin-exposed mismatch repair deficient cells

Chi Y. Shin, Isabel Mellon, Mitchell S. Turker

Research output: Contribution to journalArticlepeer-review

21 Scopus citations


Mismatch repair deficiency is known to contribute to elevated rates of mutations, particularly at mono- and dinucleotide repeat sequences. However, such repeats are often missing from the coding regions of endogenous genes. To determine the types of mutations that can occur within an endogenous gene lacking highly susceptible repeat sequences, we examined mutagenic events at the 2.3 kb mouse Aprt gene in kidney cell lines derived from mice deficient for the PMS2 and MLH1 mismatch repair proteins. The Aprt mutation rate was increased 33-fold and 3.6-20-fold for Mlh1 and Pms2 null cell lines, respectively, when compared with a wild-type kidney cell line. For the Pms2 null cells this increase resulted from both intragenic events, which were predominantly base-pairs substitutions, and loss of heterozygosity events. Almost all mutations in the Mlh1 null cells were due to base-pair substitutions. A:T→G:C transitions (54% of small events) were predominant in the Pms2 null cells whereas G:C→A:T transitions (36%) were the most common base-pair change in the Mlh1 null cells. Interestingly, 4-9% of the spontaneous mutant alleles in the mismatch repair deficient cells exhibited two well-separated base-pair substitution events. The percentage of mutant alleles with two and occasionally three base-pair substitutions increased when the Pms2 and Mlh1 null cells were treated with ultraviolet radiation (15-21%) and when the Mlh1 null cells were treated with hydrogen peroxide (35%). In most cases the distance separating the multiple base-pair substitutions on a given allele was in excess of 100 base-pairs, suggesting that the two mutational events were not linked directly to a single DNA lesion. The significance of these results is discussed with regards to the roles for the PMS2 and MLH1 proteins in preventing spontaneous and genotoxin-related mutations.

Original languageEnglish
Pages (from-to)1768-1776
Number of pages9
Issue number11
StatePublished - 2002

Bibliographical note

Funding Information:
This work was supported by NIH grants CA56383 and CA76528 (MS Turker) and GM45535 (I Mellon). Chi Shin was supported by a training core from NIEHS 1P42 ES10338. We thank Mike Liskay for providing the Pms2 and Mlh1 knockout strains, Jay Tischfield and Peter Stambrook for providing the Aprt knockout strain used in this study, and Mike Lasarev for help with statistical analysis.


  • DNA mismatch repair
  • Genetic instability
  • Genotoxin exposure
  • Multiple mutations

ASJC Scopus subject areas

  • Molecular Biology
  • Genetics
  • Cancer Research


Dive into the research topics of 'Multiple mutations are common at mouse Aprt in genotoxin-exposed mismatch repair deficient cells'. Together they form a unique fingerprint.

Cite this