title: Experimental evolution of a new enzymatic function. II. Evolution of multiple functions for ebg enzyme in E. coli.
abstract: The evolution of ebgo enzyme of Escherichia coli, an enzyme which is unable to hydrolyze lactose, lactulose, lactobionate, or galactose-arabinoside effectively, has been directed in successive steps so that the evolved enzyme is able to hydrolyze these galactosides effectively. I show that in order for a strain of E. coli with a lacZ deletion to evolve the ability to use lactobionate as a carbon source, a series of mutations must occur in the ebg genes, and that these mutations must be selected in a particular order. The ordered series of mutations constitutes an obligatory evolutionary pathway for the acquisition of a new function for ebgo enzyme. A comparison of newly evolved strains with parental strains shows that when ebg enzyme acquires a new function, its old functions often suffer; but that in several cases old functions are either unaffected or are improved. I conclude that divergence of functions catalyzed by an enzyme need not require gene duplication.
mesh_terms: D005075:Biological Evolution; D002874:Chromosome Mapping; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D005696:Galactosidases / Q000235:genetics*; D005796:Genes; D007792:Lactulose / Q000378:metabolism; D009154:Mutation; D001616:beta-Galactosidase / Q000235:genetics*
chemical_list: D007792:Lactulose; D005696:Galactosidases; D001616:beta-Galactosidase