The wild type sequence (wt; ATAAAA) was mutated and the effects of the mutants were determined by assaying the expression of the chloramphenicol acetyltransferase (CAT)-encoding gene (cat) cloned downstream. The negative mutant (neg; ACGAAA) practically abolished the activities of the 129 bp and the 416 bp elastin promoters in NIH 3T3 and neonatal rat aortic smooth muscle cells, respectively. However, when the positive mutant (pos; TATAAAA) was assayed in parallel experiments, there was enhancement of activity. The TATA box-binding protein (TBP) was shown to bind to the ATAAAA sequence and the retardation of the band was abolished by competition assay using unlabeled wt and pos sequences, but not by the neg mutant. These results provide evidence for the presence of a functional TATA box in the gene for elastin.