In eukaryotes, what factors terminate transcription by RNA polymerase II?

• A. The termination involves cleavage and polyadenylation signals and factors, with a torpedo exonuclease model helping to disengage Pol II after RNA 3' end processing.
• B. Sigma factor dissociates from RNA polymerase.
• C. Rho helicase terminates transcription.
• D. Pol II terminates after transcribing a poly-T sequence.

Answer: (D)

Transcription termination by RNA polymerase II in eukaryotes is tied to how the transcript is processed at its 3' end. The pre-mRNA contains a polyadenylation signal that’s recognized by cleavage and polyadenylation factors. They cleave the transcript and add the poly(A) tail. After this 3' end processing, a torpedo exonuclease (such as Xrn2) degrades the downstream RNA toward the polymerase. As this exonuclease catches up to Pol II, it promotes the disengagement of the polymerase from the DNA, effectively terminating transcription. This combination of coordinated 3' end processing and the torpedo mechanism is the key reason why termination occurs in this way for Pol II.

Other options point to mechanisms not used by Pol II termination in eukaryotes: sigma factors are part of bacterial transcription initiation/elongation, Rho-dependent termination is a bacterial system, and termination isn’t simply caused by transcribing a poly-T sequence.