Question

Assume that you have identified all the cis-acting sites in a prokaryotic genome for a particular trans-acting transcription factor. What is the function of this transcription factor when binding to these sites?

A. It is most likely a ligand-dependent de-repressor since the lac repressor uses this mode of regulation.
B. If the site has the sequence GATC-CTAG then it is an activator, if GATC-GATC then it is a repressor
C. Assume that it is a repressor unless it requires cAMP and then assume it is an activator like CRP-cAMP.
D. It is not possible to predict the function from the sites since could activate or repress at different sites.
E. It is most likely a ligand-dependent repressor since the trp repressor uses this mode of regulation.

Answer 1

The function of a trans-acting transcription factor binding to cis-acting sites in a prokaryotic genome can be that of an activator or a repressor, depending on the operon, specific DNA sequence, and environmental conditions.

Step-by-step explanation:

When a trans-acting transcription factor binds to cis-acting sites in a prokaryotic genome, its function at these sites can either be as an activator or a repressor of transcription. Activators increase gene transcription by facilitating RNA polymerase binding to the promoter; repressors suppress transcription by preventing RNA polymerase from transcribing the operon.

The specific sequence of nucleotides at the binding site (often at an operator or promoter) and the presence of additional molecules such as ligands or inducers determine the mode of regulation. For instance, in the case of the lac operon, the absence of glucose and the presence of lactose results in transcription activation, whereas in the trp operon, the presence of tryptophan leads to the repression of transcription.