20 Operon laktozowy, kontrola transkrypcji(1)

-lac operon-
P	0	Z	Y

Repressor binds to operator. preventing transcription of lac operon

(b) Presence of inducer

1 0	Z		Y
lac	mRNA	J		, 1

RNA-""^

polymerase

Inducer

Transcription of lac structural genes

Inducer-repressor complex does not bind to operator

Figurę 5-25 Control «f transcription of the /:. coli lac operon. (a) In the absence of an inducer such as allolactose. the lac repressor binds to the operator (O), thereby preventing RN A polymerase from transcribing the Z. Y, and A genes of the lac operon. (b) On binding inducer. the lac repressor dissociates from the operator, which permits RNA polymerase to bind to the promoter (P) and transcribc the Z. Kand A genes. fi Sec Guided Exploration 2: Regulation of gene expression by the lac repressor system