FIG. 1.
Intrachromosomal recombination reporter transgene stably integrated in pKZ1 mice. The reporter construct contains the E. coli lacZ gene situated in an inverse orientation with respect to its enhancer-promoter (EP) complex, which renders it nonfunctional. The JK5 and VK21C recombination signals that flank the lacZ gene invert it following a DNA DSB near the recombination reporter and enable lacZ transcription. The excess sequence 5′ to lacZ is removed by RNA splicing signals within exons 1 and 2 (Ex1 and Ex2). NHEJ proteins mediate the inversion of the lacZ gene into the correct orientation making this reporter a surrogate measure of DSB repair by NHEJ. Modified from Matsuoka et al. (1991).