Nucleotide sequence of a cloned cDNA for proopiomelanocortin precursor of chum salmon, Onchorynchus keta.

We have isolated a cDNA clone encoding salmon proopiomelanocortin precursor. Polyadenylated RNA was isolated from pituitary neurointermediate lobes and used to construct a cDNA library. The library was screened with 17 mer of oligodeoxyribonucleotides specific for the hexapeptide sequence in salmon beta-endorphin I, Phe-Met-Lys-Pro-Tyr-Thr at positions 4-9 excluding the third nucleotide. One positive clone, pSSM17 containing an insert of 1303 base pairs (bp) was characterized. Sequence determination revealed that it possessed sequences covering the entire regions encoding ACTH and beta-lipotropin and that the mRNA had the same overall organization as those of other mammalian species, i.e., the following peptide hormones were arranged in order from 5' upstream, ACTH including alpha-melanotropin and corticotropin-like intermediate lobe peptide, beta-lipotropin including gamma-lipotropin, beta-melanotropin and beta-endorphin. Amino acid sequences for putative salmon ACTH, beta-, and gamma-lipotropin were predicted. Comparison of the salmon mRNA sequence with those of mammals showed that the regions of alpha- and beta-MSH are relatively homologous, but other regions are much less so, especially in the 3' nontranslated region where it is much longer and completely heterologous.