A novel cis-acting regulatory element (designated BTE for basic transcription element) was found in the region proximal to the TATA sequence of the P-450c gene by the use of deletion mutations. This DNA element is considered to be involved in the basic transcription of the gene and does not show distinct enhancer activity in itself. Together with the XRE sequence (A. Fujisawa-Sehara, K. Sogawa, M. Yamane, and Y. Fujii-Kuriyama, Nucleic Acids Res. 15:4179-4191, 1987), however, this sequence is required for a high inducible expression of the P-450c gene in response to xenobiotic inducers. The BTE sequence contained the GC box consensus sequence and half of the NF-1-binding consensus or CAT box sequence, but their synthetic oligonucleotides, used as competitors in the gel mobility shift assays, did not compete with the BTE sequence for the binding protein, suggesting that the BTE sequence functions as a different recognition sequence from that for Sp1 or NF-1. Analogous sequences to BTE are found in the region promixal to the TATA sequence of other genes, especially other P-450 genes with different modes of regulation, suggesting that the BTE sequence plays a common regulatory role in basic transcription of genes including a group of the P-450 superfamily. The ubiquitous distribution of nuclear factor(s) binding to this element supports this suggestion.