Regulation of Newly Evolved Enzymes. IV. Directed Evolution of the EBG Repressor

AUTOR(ES)

Hall, Barry G.

RESUMO

In Escherichia coli, the wild-type repressor of ebg (evolved β-galactosidase) enzyme synthesis, specified by the ebgR+ gene, responds very weakly to lactulose (fructose-β-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.

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