Mapping nonselectable genes of Escherichia coli by using transposon Tn10: Location of a gene affecting pyruvate oxidase

Y. Y. Chang, J. E. Cronan

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Mutants of E. coli K-12 deficient in pyruvate oxidase were isolated by screening for the production of 14CO2 from [1-14C]pyruvate by the method of Tabor et al. One of these lesions (designated poxA) decreased the pyruvate oxidase activity to 10 to 15% of the normal level but grew well. To map this nonselectable mutation, the authors isolated strains having transposon Tn10 inserted into the chromosome close to the poxA locus and mapped the transposon. These insertions were isolated by the following procedure: pools of Tn10 insertions into the chromosomes of two different Hft strains were prepared by transposition from a λ::Tn10 vector; these Tn10-carrying strains were then mated with a poxA recipient strain, and tetracycline-resistant (Tet(r)) recombinants were selected; (iii) the Tet(r) recombinants were then screened for 14CO2 production from [1-14C]pyruvate. This method was shown to give a >40-fold enrichment of insertions of Tn10 near the poxA gene as compared with transduction. Calculations indicate that a similar enrichment should be expected for other genes. The enrichment is due to the much greater map interval over which strong linkage between selected and unselected markers is found in conjugational crosses as compared with transductional crosses. The use of Hfr conjugative transfer allows isolation of transposon insertions closely linked to a nonselectable gene by scoring hundreds rather than thousands of colonies. Using a Tn10 insertion >98% cotransduced with the poxA locus, the authors mapped the poxA gene on the E. coli genetic map. The poxA locus is located at 94 min, close to the psd locus. The clockwise gene order is ampA, poxA, psd, purA. The poxA mutation is recessive and appears to be a regulatory gene.

Original languageEnglish (US)
Pages (from-to)1279-1289
Number of pages11
JournalJournal of bacteriology
Issue number3
StatePublished - 1982

ASJC Scopus subject areas

  • Microbiology
  • Molecular Biology


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