A quiescent fibroblast in the G0/G1 phase suffers ionizing radiation-induced double-strand breaks. Repair proceeds by directly religating compatible DNA ends after a ring-shaped heterodimer binds each break and recruits a serine/threonine kinase complex. The heterodimer and kinase are:
- A RAD51 filament recruiting BRCA2
- B MRN complex (MRE11-RAD50-NBS1) recruiting ATM
- C Ku70/Ku80 heterodimer recruiting DNA-PKcs ✓
- D XPA complex recruiting TFIIH
Correct answer: C. Ku70/Ku80 heterodimer recruiting DNA-PKcs
Explanation
Nonhomologous end joining dominates double-strand break repair outside S phase. The Ku70/Ku80 heterodimer rings the broken ends, recruits DNA-dependent protein kinase catalytic subunit (DNA-PKcs), and the ends are processed by Artemis nuclease and ligated by DNA ligase IV with XRCC4. The MRN-ATM axis signals damage and RAD51-BRCA2 mediate homologous recombination, which requires a sister chromatid present only after replication. XPA-TFIIH belongs to nucleotide excision repair.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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