Transgene designed to study DNA double-strand break repair by single strand annealing (SSA). Consists of MtnB promoter/enhancer sequence upstream of a direct repeat of a 259bp genomic fragment of the MtnB transcription unit (this repeat includes MtnB UTR and coding sequence) in which the two repeats are separated by a RS(I-SceI) site, and with EGFP fused downstream of the second 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 flanking MtnB direct repeats.