CAP is said to be responsible for positive regulation of the lac operon because
A) Extracellular glucose levels influence the ability of CAP to bind to the CAP binding site.
B) CAP prevents binding of the repressor to the operator.
C) CAP bound to the CAP binding site increases the frequency of transcription initiation.
D) CAP binds the CAP binding site.
E) CAP binds cAMP.

Question

Quizplus · Accepted Answer

CAP bound to the CAP binding site increases the frequency of transcription initiation. CAP acts as an activator by binding to the CAP binding site upstream of the promoter on the lac operon. This increases the frequency of transcription initiation and leads to higher levels of lac gene expression. The binding of CAP to its binding site is enhanced by the presence of cAMP, which is produced when glucose levels are low. Thus, extracellular glucose levels indirectly influence the ability of CAP to bind to the CAP binding site, but this is not the primary mechanism by which CAP positively regulates the lac operon. CAP does not prevent binding of the repressor to the operator.

CAP Is Said to Be Responsible for Positive Regulation of the Lac