Genetics: From Genes to Genomes

Experimental evidence for repressor protein• Isolated mutant in lacI gene:• Constitutive mutant – synthesized β-galactosidaseandlac permease even in absence of lactose (inducer)• lacI must be a repressor – cells must need lacI proteinproduct to prevent expression of lacY and lacZ inabsence of inducerCopyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display17-14