Evidence that selected amplification of a bacterial lac frameshift allele stimulates Lac+ reversion (adaptive mutation) with or without general hypermutability

E. Susan Slechta, Jing Liu, Dan I. Andersson, John R. Roth

Research output: Contribution to journalArticle

33 Citations (Scopus)

Abstract

In the genetic system of Cairns and Foster, a nongrowing population of an E. coli lac frameshift mutant appears to specifically accumulate Lac+ revertants when starved on medium including lactose (adaptive mutation). This behavior has been attributed to stress-induced general mutagenesis in a subpopulation of starved cells (the hypermutable state model). We have suggested that, on the contrary, stress has no direct effect on mutability but favors only growth of cells that amplify their leaky mutant lac region (the amplification mutagenesis model). Selection enhances reversion primarily by increasing the mutant lac copy number within each developing clone on the selection plate. The observed general mutagenesis is attributed to a side effect of growth with an amplification - induction of SOS by DNA fragments released from a tandem array of lac copies. Here we show that the S. enterica version of the Cairns system shows SOS-dependent general mutagenesis and behaves in every way like the original E. coli system. In both systems, lac revertants are mutagenized during selection. Eliminating the 35-fold increase in mutation rate reduces revertant number only 2- to 4-fold. This discrepancy is due to continued growth of amplification cells until some clones manage to revert without mutagenesis solely by increasing their lac copy number. Reversion in the absence of mutagenesis is still dependent on RecA function, as expected if it depends on lac amplification (a recombination-dependent process). These observations support the amplification mutagenesis model.

Original languageEnglish (US)
Pages (from-to)945-956
Number of pages12
JournalGenetics
Volume161
Issue number3
StatePublished - 2002
Externally publishedYes

Fingerprint

Mutagenesis
Alleles
Mutation
Growth
Clone Cells
Escherichia coli
Mutation Rate
Lactose
Genetic Recombination
DNA
Population

ASJC Scopus subject areas

  • Genetics
  • Genetics(clinical)

Cite this

Evidence that selected amplification of a bacterial lac frameshift allele stimulates Lac+ reversion (adaptive mutation) with or without general hypermutability. / Susan Slechta, E.; Liu, Jing; Andersson, Dan I.; Roth, John R.

In: Genetics, Vol. 161, No. 3, 2002, p. 945-956.

Research output: Contribution to journalArticle

Susan Slechta, E. ; Liu, Jing ; Andersson, Dan I. ; Roth, John R. / Evidence that selected amplification of a bacterial lac frameshift allele stimulates Lac+ reversion (adaptive mutation) with or without general hypermutability. In: Genetics. 2002 ; Vol. 161, No. 3. pp. 945-956.
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