Transgene designed to study DNA double-strand break repair by single strand annealing (SSA). Consists of MtnB promoter/enhancer sequence followed by a 259bp genomic fragment of the MtnB transcription unit (this repeat includes MtnB UTR and coding sequence), a RS(I-SceI) site, a 208bp MtnB cDNA sequence (corresponding to the same region of the transcription unit as the 259bp genomic fragment), followed by EGFP. 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 genomic and cDNA fragments flanking the RS(I-SceI) site.