The 230/+126 bp Tnni3 promoter sequence, flanked by chicken beta-globin locus insulator sequence, is placed upstream of a beta-globin/IgG chimeric intron, nls sequence, the lacZ beta-galactosidase gene and bovine GH poly(A) signal sequence. The promoter drives expression in the embryonic myocardium of the atrioventricular canal. (J:76656)