Question

The small molecule cAMP ( red) is produced by bacteria like E. coli when nutrients are scarce. The cAMP interacts with the catabolite

activator protein (CAP; shown in dark blue). RNA polymerase is shown in light blue. Consider the interactions between CAMP, CAP, and
RNA polymerase. Which of the following statements are true?
Choose one or more:
A. Transcription increases when CAP binds to the DNA.
B. RNA polymerase binds to the promoter in the presence of cAMP.
C. RNA polymerase is activated by binding to CAP in the cytosol.
D. High cAMP levels slow the rate of transcription.

Answer 1

Transcription increases when CAP binds to the DNA. Hence the correct option is a.

In bacteria like E. coli, the small molecule cyclic AMP (cAMP) is synthesized when nutrients are scarce. This molecule plays a crucial role in regulating gene expression by interacting with the catabolite activator protein (CAP). When cAMP levels are high, cAMP binds to CAP, forming a complex that can then bind to specific DNA sequences known as cAMP response elements (CRE) in the promoter regions of target genes.

This binding of CAP-cAMP complex to DNA facilitates the recruitment of RNA polymerase (shown in light blue), enhancing its ability to initiate transcription. Therefore, statement A is correct—transcription increases when CAP binds to the DNA, illustrating how cAMP, CAP, and RNA polymerase collaborate to regulate gene expression in response to nutrient availability. The presence of cAMP and its interaction with CAP at the DNA level are essential for the efficient initiation of transcription in bacterial cells. Hence the correct option is a.