title: Analysis of relative reversion frequencies for IS2 insertion mutations in the regulatory region of the galOPETK operon of Escherichia coli.
abstract: Two previously characterized mutations in the galOPETK operon of Escherichia coli, galOP-3 and galOPE-490, contain IS2 insertions only 1 bp apart in the gal regulatory region; yet only the former yields Gal+ phenotypic revertants at a detectable frequency. We have shown that the galOPE-490 allele comprises two mutations--an IS2(I) insertion at bp+(2-6) (relative to the gal mRNA start site) plus a C/G to A/T transversion at bp + 59. The latter creates an ochre stop codon and lies within the internal site of the bipartite gal operator; it acts as an operator mutation in an in vivo repressor titration assay. Analysis of a newly isolated allele (galOP-490*) which retains the IS2 of galOPE-490 but is galE+ reveals a reversion frequency approximately 30-fold higher than that of galOP-3. Reversion of galOPE-490 is at least 10,000-fold lower and has not been detectable even under conditions conducive to enhanced double mutations in other systems.
authors.affiliation: Department of Biological Sciences, University of South Carolina, Columbia 29208.
authors.forename: R E
authors.initials: RE
authors.lastname: Musso
mesh_terms: D000483:Alleles; D004251:DNA Transposable Elements; D004926:Escherichia coli / Q000166:cytology / Q000235:genetics* / Q000378:metabolism; D005690:Galactose / Q000378:metabolism; D005798:Genes, Bacterial; D005809:Genes, Regulator; D009154:Mutation; D009876:Operon; D010957:Plasmids; D015183:Restriction Mapping
chemical_list: D004251:DNA Transposable Elements; D005690:Galactose