RNF8 was identified as a ubiquitin ligase (E3) containing a RING finger motif and a FHA domain. This protein has been shown to interact with several class II ubiquitin-conjugating enzymes including UBE2E1/UBCH6, UBE2E2, and UBE2E3. RNF8 assembles at DNA double-strand breaks (DSBs) via interactions though the FHA domain with the adaptor protein MDC1, resulting in an increase in DSB-associated H2A histone ubiquitinations mediated by the associated ubiquitin ligase RNF168 followed by the accumulation of 53BP1 and BRCA1 repair proteins. Together with RNF168, RNF8 plays an integral part of class switch recombination in B cells, allowing the production of several classes of antibodies, through the recruitment of 53BP1 and BRCA1 to the DSB sites.