From 5' to 3' the tansgene contains a synthetic polyadenylation site, the rat myosin light chain 1 gene promoter, the cre recombinase gene modified to contain a Kozak consensus site immediately upstream of the start codon, intron and polyadenylation sites from the SV40 t antigen gene, and the rat myosin light chain 1/3 enhancer. A line was chosen that exhibited skeletal muscle-specific expression as determined by Northern analysis.