A core-promoter region functions bi-directionally for human opioid-receptor-like gene ORL1 and its 5 '-adjacent gene GAIP

We report the genomic structure and functional activities of the promoter r egions of the human opioid-receptor-like gene ORL1 and its 5'-adjacent gene GAIP (G alpha interacting protein). The transcription and alternative spli cing of human ORL1 are controlled by two alternate promoters, located appro ximately 10 kb apart. The two promoter regions lack a TATA-box and are GC r ich. Promoter 1A initiates, from a single transcription start point (TSP), two transcripts: one consisting of exons 1A, 1B, 2, etc., the other without exon 1B. A potential ATG codon upstream of the initiation codon of ORL1 st arts a new open-reading frame encoding a theoretical polypeptide of 205 ami no acid residues. The promoter 1B transcribes, from multiple TSPs, only one mRNA starting with exon 1B. Two different repeat sequence polymorphisms ar e found in the ORL1 promoter regions. Luciferase reporter gene assays with promoter regions and a series of deletion mutants have mapped the core-prom oter 1A and 1B within two short fragments. DNA sequencing and a database se arch reveal that the human GAIP gene is located upstream of ORL1 and is ori ented in the opposite direction. The transcription and alternative splicing of GAIP are also under the control of alternate promoters. The first exons of ORL1 and GAIP are separated by only 83 bp. This 83 bp fragment, togethe r with short surrounding sequences from both first exons, functions bi-dire ctionally as a core-promoter for both genes. The transcription and alternat ive splicing of human ORL1 and GAIP are cell-type specific. While GAIP is e xpressed in both NT2 precursor cells and differentiated NT2 neuronal cells, ORL1 is only expressed in differentiated NT2 neurons. Since ORL1 is a G pr otein-coupled receptor and GAIP interacts with G protein alpha subunits, th eir physical linkage in the genome and co-operative transcriptional regulat ion may play a significant role in ORL1 receptor signal transduction. (C) 2 000 Academic Press.