lac absent

lac repressor synthesised in active conf; r&b operator >

operon switched off >

RNA pol unable r&b promoter, unable t/c lac operon genes; mRNA not synthesised > BG, LP, LT not produced

lac present

BG convert lac -> allolac >

allolac r&b allosteric site of lac rep, change 3D conf, becomes inactive, unable r&b operator >

operon switched on >

RNA pol able r&b promoter, able t/c lac operon genes; mRNA synthesised >

BG, LP, LT produced

low [glucose], lac present

[cAMP] inversely proportional [glucose] >

CAP activator synthesised inactive >

high [cAMP] r&b allosteric site of CAP, CAP changes 3D conf, becomes active, able r&b CAP binding site >

bends DNA, recruits RNA pol to promoter >

RNA pol binds promoter @ high affinity >

high lac operon t/c -> lactose used as temp substrate

Review: H2 Biology 17 - Regulation of GE in prokaryotes