2 DISTINCT HUMAN ENDOTHELIN-B RECEPTORS GENERATED BY ALTERNATIVE SPLICING FROM A SINGLE-GENE

A novel variant of endothelin B receptor (ETB) has been found in human brain, placenta, lung, and heart by reverse transcriptase polymerase chain reaction. This variant ETB1 has an additional 30 nucleotide sequ ence with splice sites at both ends. This results in a 10 amino acid i ncrease in the length of the second cytoplasmic domain of ETB. Polymer ase chain reaction on genomic DNA indicates that this sequence is part of the 134 bp intron which separates the second and third exons and i s contiguous with the third exon of the ETB gene. Southern blot analys is of chromosomal DNA and genomic PCR results indicate that ETB1 arise s by alternative RNA splicing of the single copy ETB gene. The insert sequence in ETB1 gene is absent in bovine, rat, and porcine DNA, and i s unique to human DNA. Both ETB and ETB1 have been expressed in hetero logous systems to examine their ligand binding and functional properti es. Reverse transcriptase polymerase chain reaction of RNA from ETB1 e xpressing cells indicates that the additional sequence is stably expre ssed.