Evolution of a new enzymatic function by recombination within a gene.
Mutations that alter the ebgA gene so that the evolved beta-galactosidase (ebg) enzyme of Escherichia coli can hydrolyze lactose fall into two classes: class I mutants use only lactose, whereas class II mutants use lactulose as well as lactose. Neither class uses galactosylarabinose effectively. In this paper we show that when both a class I and a class II mutation are present in the same ebgA gene, ebg enzyme acquires a specificity for galactosylarabinose. Although galactosylarbinose utilization can evolve as the consequence of sequential spontaneous mutations, it can also evolve via intragenic recombination in crosses between class I and class II ebgA+ mutant strains. We show that the sites for class I and class II mutations lie about 1 kilobase, or about a third of the gene, apart in ebgA. Implications of these findings with respect to the evolution of new metabolic functions discussed.
D005075:Biological Evolution; D002874:Chromosome Mapping; D004187:Disaccharides / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics*; D005696:Galactosidases / Q000235:genetics*; D005796:Genes; D007785:Lactose / Q000378:metabolism; D007792:Lactulose / Q000378:metabolism; D009154:Mutation; D011995:Recombination, Genetic; D012641:Selection, Genetic; D013379:Substrate Specificity; D001616:beta-Galactosidase / Q000235:genetics* / Q000378:metabolism
D004187:Disaccharides; D007792:Lactulose; C026793:3-O-galactosylarabinose; D005696:Galactosidases; D001616:beta-Galactosidase; D007785:Lactose