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. 2011 Feb;3(1):66–74. doi: 10.1093/jmcb/mjq055

Figure 3.

Figure 3

53BP1 and BRCA1 as regulators of the balance between NHEJ and HR. In normal cells (upper left), 53BP1 and BRCA1 together maintain an overall balance between NHEJ and HR. In BRCA1+/+; 53BP1−/− cells (upper right), 53BP1 loss inhibits NHEJ and promotes HR, resulting in increased frequency of HR-mediated repair. In BRCA1−/−; 53BP1+/+ cells (lower left), loss of BRCA1 results in a profound defect in HR, with 53BP1 now promoting NHEJ as the predominant repair pathway, resulting in genomic instability. In BRCA1−/−; 53BP1−/− cells (lower right), the loss of both BRCA1 and 53BP1 restores HR-capacity. The factors that now regulate choice between HR and NHEJ in this setting are unknown.