This Cre recombinase reporter transgene employs the "CAG promoter," which consists of the cytomegalovirus immediate early (CMV-EI) enhancer followed by a 1.3-kb DNA segment including the promoter, first exon and first intron of the chicken beta-actin gene, with the 3' splice junction sequence replaced by that of the rabbit hemoglobin beta gene. The promoter is separated from the bacterial beta-galactosidase (lacZ) coding sequence, with a rabbit globin polyadenylation signal, by a loxP-flanked chloramphenicol acetyltransferase (cat) gene with the SV40 small t intron and polyadenylation signal. ELISA demonstrated high-level expression of CAT protein in heart and muscle and lower levels in other tissues of transgenic mice. (J:75287)