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Updated: May 15, 2026

Visualizing Single-Stranded DNA Foci in the G1 Phase of the Cell Cycle
Published on: December 22, 2023
RPA accumulation during class switch recombination represents 5'-3' DNA-end resection during the S-G2/M phase of the
Arito Yamane1, Davide F Robbiani, Wolfgang Resch
1Genomics & Immunity, NIAMS, National Institutes of Health, Bethesda, MD 20892, USA.
Abstract:
Activation-induced cytidine deaminase (AID) promotes chromosomal translocations by inducing DNA double-strand breaks (DSBs) at immunoglobulin (Ig) genes and oncogenes in the G1 phase. RPA is a single-stranded DNA (ssDNA)-binding protein that associates with resected DSBs in the S phase and facilitates the assembly of factors involved in homologous repair (HR), such as Rad51. Notably, RPA deposition also marks sites of AID-mediated damage, but its role in Ig gene recombination remains unclear. Here, we demonstrate that RPA associates asymmetrically with resected ssDNA in response to lesions created by AID, recombination-activating genes (RAG), or other nucleases. Small amounts of RPA are deposited at AID targets in G1 in an ATM-dependent manner. In contrast, recruitment in the S-G2/M phase is extensive, ATM independent, and associated with Rad51 accumulation. In the S-G2/M phase, RPA increases in nonhomologous-end-joining-deficient lymphocytes, where there is more extensive DNA-end resection. Thus, most RPA recruitment during class switch recombination represents salvage of unrepaired breaks by homology-based pathways during the S-G2/M phase of the cell cycle.
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