Transcription of the rat alpha 1B adrenergic receptor gene in liver is controlled by three promoters.

The proximal 5'-flanking region of the rat alpha 1B adrenergic receptor (alpha 1BAR) gene contains discrete transcription start points (tsp) utilized in liver, located at -54, -57 (tsp1), and -443 base pairs (tsp2) upstream from the translation start codon (Gao, B., and Kunos, G. (1993) Gene (Amst.) 131, 243-247). Primer extension analyses using 5' upstream primers now identify an additional cluster of tsp between -1035 and -1340 base pairs (tsp3). Northern blots of rat liver mRNA reveal three alpha 1BAR mRNAs of 2.3, 2.7, and 3.3 kilobases in length. Transient transfections of putative promoter/pCAT constructs document the existence of three promoters, P1 (-127, -49), P2- (-813, -432), and P3 (-1363, -1107), which direct transcription from tsp1, tsp2, and tsp3, respectively. P1 contains no recognition sequences for known transcription factors. P2 is (G + C)-rich, lacks a TATA box, and contains a cAMP response element, GC, CACC, and GCAAT boxes, and binding sites for nuclear factor I. P3 contains a putative TATATA and CCAAT box and is flanked by recognition sites for the liver-specific CCAAT/enhancer binding protein and hepatocyte nuclear factor 5. These findings indicate that heterogeneity of alpha 1BAR mRNA in liver is related to transcription of the gene by three distinct promoters. Differential control of these promoters may underlie the well documented developmental and tissue-specific regulation of the alpha 1BAR.