Using a rat alpha 1B adrenergic receptor(AR)-encoding cDNA probe, we isolated two genomic clones from a rat liver genomic DNA library. Southern blot analysis and nucleotide sequencing indicate that the rat alpha 1B AR gene has two exons and a single large intron of at least 16 kb. Analysis of the sequence of the 5'-flanking region suggests that this gene has the features of a housekeeping gene: it has neither a TATA box nor a CAAT box, but has multiple transcription start points (tsp), multiple Sp1-binding sites, and a high G + C content. The 5'-flanking region also contains consensus sequences for AP1- and AP2-binding sites, and putative sites for cyclic AMP (CRE), glucocorticoid (GRE), and thyroid responses (TRE). The 3'-flanking region contains a putative polyadenylation signal (ATTAAA) 492 bp downstream from the stop codon. A comparison of the rat alpha 1B AR sequence with that of the recently cloned human alpha 1B AR gene showed that the overall structure of this gene is highly conserved, with some notable differences in the 5'-flanking region.