2 TYPES OF CDNAS ENCODING PROOPIOMELANOCORTIN OF SOCKEYE-SALMON, ONCORHYNCHUS-NERKA

To investigate regulatory mechanisms of proopiomelanocortin (POMC) gen e expression in sockeye salmon, we have isolated and characterized cDN As encoding two types of sockeye salmon POMC, which are referred to as ssPOMC-A and -B. Two types of PCR products were amplified from total RNA of sockeye salmon pituitaries by use of rainbow trout sequences. F ull length cDNA clones encoding ssPOMC-A and ssPOMC-B were obtained fr om a pituitary cDNA library of sockeye salmon using the PCR products a s probes. The ssPOMC-A and -B cDNAs have a length of 1072 and 1709 bps , respectively. Northern blot analysis showed that both ssPOMC-A and - B mRNAs were expressed only in the pituitary, and their sizes were abo ut 1.2 kb and 1.8 kb, respectively. The presence of two ssPOMC genes w as confirmed by Southern blot analysis of genomic DNA obtained from a single sockeye salmon. The deduced amino acid sequences of the ssPOMC- A and -B contained 230 and 226 residues, respectively. The amino termi nal of beta-endorphin in ssPOMC-B which corresponds to Met-enkephalin domain is YSGFM, which is different from YGGFM of Met-enkephalin found in many other vertebrate species. The homology of nucleotide sequence s between ssPOMC-A and -B is 59% in the entire coding region, whereas alpha-MSH coding regions are highly homologous (91%). Although the ded uced amino acid sequences of ssPOMCs show 43% overall similarity, thei r hydropathy profiles are coincident with those of several other verte brate species, particularly the amino terminal of N-terminal peptide ( NPP) shows almost the same pattern with other vertebrate NPPs.