title: Evolution of a second gene for beta-galactosidase in Escherichia coli.
abstract: Mutants of E. coli K12 with deletions of the beta-galactosidase gene (lacZ) can reacquire the ability to hydrolyze beta-galactosides during prolonged intense selection for growth on lactose. Full lactose competence is restored through a sequence of at least five mutations. Cell extracts of these derived strains hydrolyze o-nitrophenyl-beta-D-galactoside, the standard substrate for assay of beta-galactosidase. The enzyme responsible for this activity differs in its immunological, kinetic, and sedimentation characteristics from the lacZ beta-galactosidase of wild-type E. coli. Its genetic determinant, designated ebg-5, maps at 59 min on the E. coli chromosome, whereas the lac operon maps at 10 min. We suggest that a gene not involved in lactose utilization has been progressively changed into a form capable of specifying a beta-galactosidase and that this process is similar to that whereby genes with new functions are evolved by natural selection.
mesh_terms: D002499:Centrifugation, Density Gradient; D002874:Chromosome Mapping; D000939:Epitopes; D004926:Escherichia coli / Q000201:enzymology* / Q000378:metabolism; D005696:Galactosidases / Q000096:biosynthesis* / Q000302:isolation & purification; D005796:Genes; D007785:Lactose / Q000378:metabolism; D009154:Mutation; D014161:Transduction, Genetic
chemical_list: D000939:Epitopes; D005696:Galactosidases; D007785:Lactose