Structural differences in 5'-flanking regions of rat cytochrome P-450aldo and P-450(11) beta genes

Two rat genomic clones, one for cytochrome P-450aldo and the other for P-450(11) beta, were isolated and characterized. The two genes, encoding structurally homologous proteins, were closely similar in their intron-exon organizations. Their 5'-flanking regions, however, contained only a few homologous regions. A putative cyclic AMP responsive element, TGACGTGA, was found in the P-450aldo gene, but this sequence was altered at two positions in the P-450(11) beta gene. S1 nuclease protection assay revealed a single transcription initiation site for the P-450aldo gene, while multiple sites were found for the P-450(11) beta gene. These results suggest that transcriptional regulation of the rat P-450aldo and P-450(11) beta genes is due to differences in the sequences of their 5'-flanking regions.