PCR screening strategy. a) A 3.9 kb PCR band occurs in the non-targeted wild type rhesus macaque fibroblast DNA. The reverse screening primer anneals to the deleted part of exon 6. If a targeting event has occurred, there will be no 3.9 kb PCR band since that part if exon 6 has been deleted. b) M = 1 kb Marker, HTF = HPRT targeted fibroblasts, WT = wild type rhesus fibroblasts, ATM = ataxia telangiectasia mutated (positive control).