Rho-dependent termination in E. coli: Which statements about the mechanism are correct?

Introduction / Context:
Termination of transcription in bacteria can be intrinsic (Rho-independent) or Rho-dependent. Knowing the requirements for Rho-dependent termination clarifies how certain transcripts are selectively terminated.

Given Data / Assumptions:

• Rho is an RNA-dependent ATPase/helicase.
• Rho binds specific RNA regions (rut sites) that are typically C-rich and unstructured.

Concept / Approach:
Rho loads onto the nascent RNA at a rut site and translocates 5'→3' along the RNA using ATP. When RNA polymerase pauses downstream, Rho catches up and promotes dissociation of the transcription complex, releasing RNA.

Step-by-Step Solution:
Confirm ATP requirement → Rho translocation consumes ATP. Confirm RNA features → rut sites often ~50 nt, C-rich, and relatively unstructured to allow Rho loading. Select the combined answer acknowledging both requirements.

Verification / Alternative check:
Mutations that disrupt rut sites or ATPase activity of Rho impair termination; transcriptional pausing elements enhance Rho catch-up.

Why Other Options Are Wrong:
Option d contradicts the release function; option e confuses promoter strength with termination determinants.

Common Pitfalls:
Mixing intrinsic terminators (hairpin + poly-U) with Rho-dependent mechanisms; assuming Rho acts without energy.

Final Answer:
Both (a) and (b).