Transgene designed to study DNA double-strand break repair by single strand annealing (SSA). Consists of MtnB promoter/enhancer sequence followed by a 129bp MtnB cDNA fragment, a RS(I-SceI) site, a 129bp homologous MtnD cDNA fragment (sharing 81% sequence identity with the MtnB fragment), with EGFP fused downstream of the MtnD sequence. In this configuration, the EGFP protein is not expressed. EGFP protein is only expressed if a double-strand DNA break is induced at the RS(I-SceI) site by the I-SceI endonuclease, and the break is repaired by single strand annealing (SSA) of the MtnB and MtnD fragments flanking the RS(I-SceI) site.