Cloning and Sequencing of cDNA for Akazara Scallop Tropomyosin

cDNA clones encoding tropomyosin of akazara scallop Chlamys nipponensis akazara striated adductor muscle were isolated and sequenced. The largest cDNA obtained is composed of 1, 995 bp including an open reading frame of 852 bp at nucleotide positions 27-878, which deduced amino acid sequence of 284 residues with a calculated molecular weight of 32, 540. According to database searches on NBRF-PIR 49.0 and GenBank, the amino acid sequence showed higher homology of 73% and 70% to bloodfluke planorb tropomyosin and mussel anterior byssus retractor muscle tropomyosin, respectively, and considerably high homology of 53% and 51% to rabbit α- and β-tropomyosins, respectively. The sequences corresponding to the critical region for actin-binding (residues 1-9) and troponin-T-binding region (near residues 150-180) of rabbit α-tropomyosin are conserved also in akazara scallop tropomyosin. As the nine residues at both of the N-terminus and C-terminus are generally regarded to form a head-to-tail interaction region, the residues at the N-terminus of akazara scallop tropomyosin show high sequence homology to those of various muscle tropomyosins. However, those at the C-terminus show lower sequence homology than those of vertebrate tropomyosin. Thus, head-to-tail interaction of akazara scallop tropomyosin may be different from rabbit tropomyosin on account of low homology of the C-terminal sequence.