Efficient and muscle-specific gene expression can be obtained with constructs containing two or more copies of USE and/or ΔUSE fused to the minimal promoter of the TnISlow gene. USE is a small (about 160-bp) upstream enhancer of the TnISlow gene that confers slow-twitch muscle fiber specificity. ΔUSE is generated from a 100-bp deletion at the 5′ end of USE. ΔUSE confers expression in slow- and fast-twitch muscle fibers. The strength and relatively small size (less than 600-bp) of these constructs make them useful for gene therapy applications.
