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The effect of genomic position on reversion of a lac frameshift mutation ( lacIZ33 ) during non‐lethal selection (adaptive mutation)
Author(s) -
Slechta E. Susan,
Harold Jennifer,
Andersson Dan I.,
Roth John R.
Publication year - 2002
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.2002.02934.x
Subject(s) - reversion , biology , plasmid , adaptive mutation , genetics , mutant , mutation , operon , frameshift mutation , lac operon , gene duplication , point mutation , gene , phenotype , genetic algorithm , machine learning , computer science
Summary In a system described by Cairns and Foster, starvation of a particular leaky lac mutant ( lacIZ33 ) in the presence of lactose appears to direct mutation in non‐growing cells to sites that allow growth (adaptive mutation). This behaviour requires that the lac operon be located on an F ′ plasmid. This position effect was investigated by placing the mutant lac operon at many sites in the genome of Salmonella enterica ( Typhimurium ; LT2) and testing reversion behaviour. Genomic position did not affect reversion during non‐selective growth. When lac was at any of 550 chromosomal sites, starvation caused little or no enhancement of reversion. In the 28 strains with the lac on Salmonella ’s conjugative plasmid (pSLT), selection enhanced reversion strongly, just as seen for strains with lac on an F ′ plasmid. In 46 strains, the lac operon was inserted within a small chromosomal duplication, and selection stimulated RecA‐dependent partial reversion by simple amplification (about 8 × ) of the mutant lac region. The position of lac on a conjugative plasmid is important to reversion because it allows more frequent gene duplication and amplification. These events are central to growth and reversion under selection because they increase the number of replicating lac alleles within each developing revertant clone.