A 6.5 kb genomic DNA fragment of the Ckmm gene containing the promoter and enhancer 1, untranslated exon 1, 3kb of intron 1 including the enhancer 2 region, and the first 16 bp of exon 2 drives expression of a modified cre with an SV40 large T antigen nuclear localization signal. Expression is directed to the heart and skeletal muscle. (J:51266)