Transcription of a bacterial operon reaches a terminator sequence that lacks a GC-rich hairpin followed by a run of U residues. Termination still occurs when a hexameric protein, having bound a C-rich unpaired rut site on the nascent RNA, catches up to the paused polymerase and unwinds the RNA-DNA hybrid. This protein is:

• A Sigma factor
• B NusG
• C Rho factor ✓
• D Rho-independent release factor

Explanation

Rho factor is an ATP-dependent hexameric helicase-translocase that mediates intrinsic-factor-independent termination. It binds a C-rich, poorly structured rut (rho utilization) site on the naked nascent RNA, translocates along the RNA using ATP, and on reaching the paused polymerase unwinds the RNA-DNA hybrid, releasing the transcript. Sigma factor functions only at promoters during initiation, and hairpin-plus-poly-U signals define rho-independent termination.

Reference: Lehninger Principles of Biochemistry, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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