The CAG promoter is a strong synthetic promoter frequently used to drive high levels of gene expression in mammalian expression vectors. CAG promoter was constructed in the lab of Dr Jun-ichi Miyazaki from the following sequences: (C) the cytomegalovirus (CMV) early enhancer element,(A) the promoter, the first exon and the first intron of chicken beta-actin gene,(G) the splice acceptor of the rabbit beta-globin gene