Department of Pharmacology, Umeå University, Sweden.
We here describe the cloning of an additional gene, called alpha 2-1.8, which is similar to the previously cloned human alpha 2-adrenergic receptor located on chromosome 4. The alpha 2-1.8 gene was identified by using the polymerase chain reaction with primers specific for sequences in transmembrane regions 2 and 5 of the previously isolated human alpha 2-C4 and alpha 2-C10 adrenoceptor genes, which are localized on chromosomes 4 and 10, respectively. The new gene was identified by amplifying the 1.8 kb size fractionated region of PstI restriction cut human genomic DNA. The previously cloned alpha 2-C10 and alpha 2-C4 genes were recovered at their expected locations, 0.96 and 5.9 kb, respectively. We have identified 387 bases of the new alpha 2-1.8 gene, and its sequence is identical to the previously described alpha 2-C4 gene, but it is distinct from the alpha 2-C10 and alpha 2-C2 genes. Our results demonstrate that the alpha 2-C4 adrenergic receptor exists in more than one copy in the human genome.