Genomic organization of the rat pituitary adenylate cyclase-activating polypeptide receptor gene. Alternative splicing within the 5'-untranslated region.

Pituitary adenylate cyclase-activating polypeptide (PACAP) elicits its diverse biological actions by interacting with both PACAP-selective type I PACAP receptors (PACAPRs) and type II PACAPRs that do not distinguish between PACAP and vasoactive intestinal polypeptide. Using long distance polymerase chain reaction, we amplified and characterized the entire coding region of the rat type I PACAPR (rPACAPR) gene, which spans 40 kilobases and contains 15 exons. Mapping of the exons and sequencing of all intron-exon boundaries revealed a structural organization of the rPACAPR gene that is very similar to those encoding other members of the calcitonin/secretin/parathyroid hormone receptor family. Southern blot analysis demonstrated a single copy of the rPACAPR gene. A combination of rapid amplification of cDNA ends and reverse transcriptase polymerase chain reaction revealed an unexpected diversity in the rPACAPR mRNA in the 5'-untranslated (5'-UTR) region. Four rPACAPR cDNAs were identified with 5'-UTR sequences that all diverged from the genomic sequence at a site 76 bp upstream of the ATG start codon, where a consensus 3' slice acceptor sequence was located. Sequence analysis of these amplified transcripts demonstrated that they arise by tissue-specific differential usage of four exons in the 5' noncoding region of the rPACAPR gene. This study is the first to elucidate the structural organization of a PACAPR gene and to demonstrate that alternative splicing generates rPACAPR transcripts with unique 5'-UTRs.