glucose lactose operator (repressor binding site) PromoterZYA lacZ lacY lacAcrp lacI repressor active activator inactive PromoterIPromotercrp + - mRNA mRNA activator binding site polymerase RNA polymerase RNA operator (repressor binding site) PromoterZYA lacZ lacY lacAcrp lacI repressor active repressor lactose inactive activator inactive cAMP activator active PromoterIPromotercrp mRNA mRNA mRNA LacZ (?gal) LacY LacA activator binding site polymerase RNA polymerase RNA repressor active can metabolize lactose!cAMP + - + lactose + cAMP activator active polymerase RNA DNA DNA The lac operon: a model of gene regulation in E. coli MIT OpenCourseWare http://ocw.mit.edu 7.01SC Fundamentals of Biology Fall 2011