Correct option is D
Double-strand break repair (DSBR) in prokaryotes primarily occurs through homologous recombination. The stepwise recruitment of proteins follows this sequence:
RecBCD Complex Initiation (First Step)
- RecBCD is a helicase-exonuclease complex that binds to the DNA break site and starts end resection.
- It unwinds the DNA and generates 3′ single-stranded DNA (ssDNA) overhangs required for homologous recombination.
Ssb Binding (Second Step)
- Single-strand binding protein (Ssb) coats the newly formed ssDNA to stabilize it and prevent secondary structures.
RecA Loading (Third Step)
- RecA protein replaces Ssb on ssDNA and forms a nucleoprotein filament, which is crucial for strand invasion into a homologous DNA sequence.
DNA Polymerase III Activity (Fourth Step)
- DNA Pol III synthesizes new DNA to replace the degraded or damaged strand using the invaded homologous sequence as a template.
DNA Ligase Sealing (Final Step)
- DNA Ligase seals the nicks in the sugar-phosphate backbone, completing the repair process.
Information Booster
RecBCD Complex:
- Functions as a helicase-exonuclease.
- Generates ssDNA overhangs required for recombination.
- Regulated by the Chi (χ) sequence, which influences RecA loading.
Ssb (Single-Strand Binding Protein):
- Binds to single-stranded DNA and prevents degradation.
- Facilitates RecA filament formation.
RecA:
- Facilitates homologous strand invasion into an intact DNA molecule.
- Forms a nucleoprotein filament for recombination.
DNA Polymerase III:
- Fills in the missing DNA sequence using the homologous strand as a template.
DNA Ligase:
- Seals the final nicks, completing DNA repair.
Significance of DSBR:
- Prevents mutations and chromosomal rearrangements.
- Essential for genome stability in bacteria.
Role in Antibiotic Resistance:
- Homologous recombination-based repair can integrate foreign DNA, contributing to bacterial evolution and resistance mechanisms.
