lac operon transcription regulation

(a) When glucose is available and lactose is unavailable, lac operon genes are not transcribed. (b) Lactose availability in the absence of glucose induces activated transcription of operon genes by binding of the CAP–cAMP complex at the CAP site (see the text for a description). (c) The presence of both glucose and lactose leads to basal transcription of the operon(a) When glucose is available and lactose is unavailable, lac operon genes are not transcribed. (b) Lactose availability in the absence of glucose induces activated transcription of operon genes by binding of the CAP–cAMP complex at the CAP site (see the text for a description). (c) The presence of both glucose and lactose leads to basal transcription of the operon

(a) Lactose unavailable (glucose available) Repressor No gene transcription 1 CAP bfiding site - mRNA 1 / l Lac repressor protein binds to l the operator (/acO) sequence WRepre'ssor l and inhibits transcription protein (b) Lactose available (glucose unavailable) RNA polymerase Repressor CAP binding site Activated gene A transcnpuon l i R i @ Transcription - mRNA mRNA — l Translation 1 l l Transacetylase Repressor Permease protein figalactosidase 1/0 Allolactose « \Mth repressor protein inactivated by \1 allolactose binding, RNA polymerase i carries out transcription ‘ Inducer-repressor complex (c) Lactose and glucose available Repressor Basal 1 CAP binding site i Transcription - mRNA mRNA :1:!: Translation 1 l l C Allolactose Transacetylase Permease B—galactosidase Repressor protein