cDNA cloning and sequence of European sea bass (Dicentrarchus labrax) somatolactin

Three cDNA clones encoding for European sea bass somatolactin (SL) were obt ained by RT-PCR and 3' RACE of RNA of pituitary origin. Clone 1 was 582 bp in length, and included a part of the signal peptide and the 5' end of the mature protein. Clone 2 (1075 bp) included a fragment of the coding sequenc e and the 3' untranslated region, which was 888 bp in length and contained two putative polyadenylation signals (AATAAA) at 12-17, and 202-207 nucleot ides upstream of the poly (A) tail. Clone 3 was 624 bp in length and its nu cleotide sequence encoding for the entire mature protein confirmed the sequ ence already determined from the first two clones. The size of SL mRNA tran scripts was estimated by Northern blot analysis and a single band of approx imately 1.6 kb was observed with pituitary RNAs. No band was found with RNA s of brain and liver origin. Alignment of the deduced amino acid sequence r evealed that European sea bass SL shared 90-84% identity with perciform, pl euronectiform and scorpaeniform fish SLs, and 77-57% with other SLs of more distant fish orders, with a strict conservation of Cys residues and the N- glycosylation site (Asn-Lys-Thr) at 121-123 amino acid positions. The recon struction of the phylogenetic tree based on SL nucleotide sequences, and an alyzed by maximum likelihood distances, showed the same clustering as the p resent hierarchy of fish. When comparisons were made among SL, prolactin an d growth hormone of European sea bass, the overall amino identity was relat ively low (22-23%). However, a high degree of amino acid homology was found at the C-terminus, which contains three of the four Cys residues strictly conserved in all the members of GH/PRL family. (C) 2000 Elsevier Science In c. All rights reserved.