Which Protein Catalyzes Branch Migration Activity in the Holliday Junction?

The Holliday junction (HJ) is a critical intermediate structure formed during homologous recombination, a process essential for DNA repair, genetic diversity, and proper chromosome segregation. A key step in processing the Holliday junction is branch migration, where the crossover point moves along the DNA, extending the region of strand exchange.

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Proteins Involved in Holliday Junction Branch Migration

In Escherichia coli and many prokaryotes, the RuvAB protein complex is responsible for catalyzing branch migration of the Holliday junction:

• RuvA binds specifically to the Holliday junction, stabilizing the structure and recruiting RuvB.

• RuvB is an ATPase motor protein that forms a hexameric ring around DNA and uses energy from ATP hydrolysis to translocate DNA strands, driving branch migration.

• The complex works together to move the junction along the DNA, facilitating strand exchange.

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Explanation of the Options

1. Spo11

   • Spo11 is an enzyme that catalyzes the formation of double-strand breaks to initiate meiotic recombination but does not catalyze branch migration.

2. RuvB

   • Correct answer. RuvB is the motor protein that drives branch migration by translocating DNA through the Holliday junction.

3. Zip1

   • Zip1 is a component of the synaptonemal complex in eukaryotes, involved in chromosome pairing during meiosis, not branch migration.

4. RuvC

   • RuvC is an endonuclease that resolves the Holliday junction by cleaving the DNA strands after branch migration has occurred but does not catalyze branch migration itself.

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Supporting Evidence from Research

• Cryo-EM structures and biochemical studies reveal that RuvB assembles into a hexameric ring that encircles DNA and uses ATP hydrolysis to power branch migration2.

• RuvAB complex promotes rapid, unidirectional branch migration of Holliday junctions in E. coli18.

• RuvC acts downstream to resolve the junction by symmetrical cleavage3.

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Keywords for SEO Optimization

• Holliday junction branch migration

• RuvB ATPase motor protein

• RuvAB complex in E. coli

• DNA recombination intermediates

• Homologous recombination proteins

• DNA strand exchange and migration

• RuvC resolvase function

• Spo11 meiotic DSB formation

• Zip1 synaptonemal complex

• DNA repair and recombination

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Conclusion

Among the proteins listed, RuvB is the key ATPase motor protein that catalyzes branch migration of the Holliday junction during homologous recombination. Spo11 initiates recombination by creating breaks, Zip1 functions in chromosome pairing, and RuvC resolves the junction by cleavage but does not promote branch migration.

Correct answer: (2) RuvB