Clusters of mutations from transient hypermutability

Proc Natl Acad Sci U S A. 2005 Sep 6;102(36):12849-54. doi: 10.1073/pnas.0503009102. Epub 2005 Aug 23.


Collections of mutants usually contain more mutants bearing multiple mutations than expected from the mutant frequency and a random distribution of mutations. This excess is seen in a variety of organisms and also after DNA synthesis in vitro. The excess is unlikely to originate in mutator mutants but rather from transient hypermutability resulting from a perturbation of one of the many transactions that maintain genetic fidelity. The multiple mutations are sometimes clustered and sometimes randomly distributed. We model some spectra as populations comprising a majority with a low mutation frequency and a minority with a high mutation frequency. In the case of mutants produced in vitro by a bacteriophage RB69 mutator DNA polymerase, mutants with two mutations are in approximately 10-fold excess and mutants with three mutations are in even greater excess. However, phenotypically undetectable mutations seen only as hitchhikers with detectable mutations are approximately 5-fold more frequent than mutants bearing detectable mutations, indicating that they arose in a subpopulation with a higher mutation frequency. Excess multiple mutations may contribute critically to carcinogenesis and to adaptive mutation, including the adaptations of pathogens as they move from host to host. In the case of the rapidly mutating riboviruses, the viral population appears to be composed of a majority with a mutation frequency substantially lower than the average and a minority with a huge mutational load.

Publication types

  • Research Support, N.I.H., Intramural

MeSH terms

  • Animals
  • Bacteriophages / enzymology
  • DNA Mutational Analysis
  • DNA-Directed DNA Polymerase / metabolism
  • Evolution, Molecular*
  • Genome
  • Humans
  • Mutagenesis / genetics*
  • Mutation / genetics*
  • Neoplasms / genetics
  • RNA / genetics


  • RNA
  • DNA-Directed DNA Polymerase