Figure 1  Recombination substrates used for assaying homology-directed repair. Cutting at the I-SceI site within the mutant GFP (SceGFP) results in a double-strand break that can be repaired through homologous gene conversion using a 3'-truncated copy of GFP as sequence donor. The mechanism results in the formation of a functional copy of the GFP gene. The model shown assumes gene conversion occurs via the synthesis-dependent annealing mechanism. Moynahan et al [24] have used such a GFP recombination substrate to demonstrate that cells with defective BRCA2 protein are deficient in their ability to repair the I-SceI-induced DSB through homologous recombination.