Transgene designed to study DNA double-strand break repair by single strand annealing (SSA). Consists of MtnB promoter/enhancer sequence followed by a direct repeat of a 208bp fragment of MtnB cDNA sequence in which the two repeats are separated by a RS(I-SceI) site, and with EGFP fused downstream of the second repeat. A silent point mutation has been introduced into the promoter distal direct repeat. 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 cDNA fragments flanking the RS(I-SceI) site.