Piscine (Sparus aurata) α subunit of the G-protein transducin is homologous to mammalian cone and rod transducin

Abstract

A novel cDNA encoding α subunit of the GTP-binding protein, transducin, has been cloned from a marine fish, Sparus aurata. The cDNA contains an open reading frame of 1050 nt (encoding 350 amino acid residues). A high degree of identity was found with known mammalian transducin proteins of cones (Gt2α) or rods (Gt1α): human Gt2α (80.2%), bovine Gt2α (79.3%), mouse Gt1α (78.2%), mouse Gt2α (78%) and bovine Gt1α (77.9%). Northern blot analysis of different tissues revealed a transcript of about 2.5 kb, which is expressed only in the fish eye and not in other tissues from adult fish, supporting its identification as transducin. Ontogeny of transducin mRNA expression during early development of Sparus aurata, determined by Northern blot analysis, showed very low levels in larvae 3 days after hatching but not earlier. Levels increased 3- and 6-fold on days 4 and 6 (respectively) compared with those on day 3 and remained essentially unchanged thereafter, until day 21 after hatching (the last day studied). Our results suggest that in fish only one α subunit of transducin is found, which shows similar identity with cone and rod α subunits of mammals.