title: Regulation of newly evolved enzymes. IV. Directed evolution of the Ebg repressor.
abstract: In Escherichia coli, the wild-type repressor of ebg (evolved beta-galactosidase) enzyme synthesis, specified by the ebgR+ gene, responds very weakly to lactulose (fructose-beta-D-galactopyranoside). Selection for a functional repressor that responds strongly to lactulose as an inducer reveals the existence of ebgR+L mutants, which occur spontaneously at a frequency of about 2 X 10(-10) . EBGR+L mutants are pleiotropic in that they specify ebg repressor with a greatly increased response to lactulose, lactose, galactose-arabinoside and methyl-galactoside as inducers. Selection of ebgR+L mutants is discussed within the framework of directed evolution of a regulatory function.
mesh_terms: D005075:Biological Evolution; D004794:Enzyme Repression; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism; D005690:Galactose / Q000378:metabolism; D005696:Galactosidases / Q000235:genetics*; D005809:Genes, Regulator; D007785:Lactose / Q000378:metabolism; D009154:Mutation; D012641:Selection, Genetic; D001616:beta-Galactosidase / Q000235:genetics*
chemical_list: D005696:Galactosidases; D001616:beta-Galactosidase; D007785:Lactose; D005690:Galactose