The 638/-138 bp rat Nppa regulatory region sequence, containing silencer and enhancer sequences, is placed upstream of the 230/+126 bp Tnni3 promoter sequence (and the chimeric silencer-promoter is flanked by chicken beta-globin locus insulator sequence), followed by a beta-globin/IgG chimeric intron, nls sequence, the lacZ beta-galactosidase gene and bovine GH poly(A) signal sequence. The Nppa regulatory sequence drives expression in the embryonic atrial and ventricular chamber myocardium but represses expression in the atrioventricular canal. (J:76656)