Question

Which of the following promotes branch migration at higher rates than does Rec-A?

• A. Rec-B
• B. Rec-C
• C. Rec-D
• D. Ruv-A and Ruv-B

Hint:

Ruv-A and Ruv-B proteins are key to promoting efficient branch migration during recombination, allowing the recombination process to proceed at higher rates.

Answer 1

The Correct Option is D

Rec-B, Rec-C, and Rec-D are all subunits of the RecBCD complex, which acts earlier in recombination to unwind and resect DNA ends so RecA can load -- none of them is the motor that drives branch migration itself.

RuvA recognizes the Holliday junction and recruits RuvB, an ATP-powered motor protein, and together they actively pump the junction along the DNA duplex, driving branch migration considerably faster than RecA alone can manage.

So the protein pair that promotes branch migration at a higher rate than RecA is Ruv-A and Ruv-B.

Answer 2

Separating these options into "motor" proteins versus "structural/processing" proteins clarifies the answer.

1. Rec-B: Functions as a helicase-nuclease during end resection, a structural/processing role that precedes the recombination synapse, not a dedicated branch-migration motor.
2. Rec-C: Provides Chi-site recognition within RecBCD, a targeting function rather than a migration-driving one.
3. Rec-D: Supplies additional helicase activity within RecBCD for end processing, again before the junction/migration stage.
4. Ruv-A and Ruv-B: This pair forms a dedicated ATP-hydrolysing motor complex assembled directly onto the Holliday junction, purpose-built to translocate the junction along DNA -- a far more specialized and efficient migration engine than RecA's more general recombinase activity.

Only the RuvAB complex is a purpose-built branch-migration motor, explaining why it outpaces RecA at this specific task.

So, the correct answer is Ruv-A and Ruv-B.