lac Operon Genes and RegulatorySequences

Table 12.2 lac Operon Genes and Regulatory Sequences Gene/Sequence Product/Sequence Type Protein-Producing Genes lac! Repressor protein IacZ B-galactosidase IacY Permease IacA Transacetylase Regulatory Sequences IacO Operator IacP Promoter Function Contains two binding sites, one for the operator and one for allolactose, the inducer. Cleaves lactose into two monosac- charides (glucose and galactose). Facilitates lactose transport across the cell membrane. Protects against harmful by-products of lactose metabolism. Binds repressor protein to block transcription of operon genes. Binds RNA polymerase. Important Mutants I‘: Unable to bind to operator. ls: So-called super repressor. Unable to bind the inducer (allolactose), blocking all transcription. Z": No functional B-galactosidase. Y‘: No functional permease. A‘: No transacetylase. OC: Fails to bind repressor protein, resulting in continuous (constitutive) transcription. P”: Fails to bind RNA polymerase or does so weakly.