Cloning of the lkyB (tolB) gene of Escherichia coli K12 and characterization of its product.

The lkyB gene of Escherichia coli K12 has been cloned from the Clarke and Carbon colony bank by selecting a ColE1 plasmid conferring cholic acid resistance to lkyB mutants. The lkyB gene was localized on hybrid plasmid pJC778 by analysis of mutated plasmids generated by Tn5 insertions. Restriction analysis and complementation studies indicated that plasmid pJC778 carried genes nadA, lkyB and sucA which mapped at min 16.5; the lkyB+ allele was dominant over the lkyB207 mutant allele. Analysis of cell envelope proteins from strains carrying plasmids pJC778 (lkyB+), pJC2578 or pJC2579 (lkyB::Tn5), as well as plasmid-coded proteins in a maxicell system, made it likely that the ikyB gene product was a membrane protein of molecular weight 42,000.