The RT PCR approach was used to obtain the nucleotide sequence of the mRNA of a sarco/endoplasmic reticulum calcium transporting ATPase (SERCA) from the cross-striated (phasic) part of the adductor muscle of the deep sea scallop. Initially, degenerate primers based on consensus sequences among SERCAs and tryptic fragments of the scallop Ca-ATPase were used. The sequence was then extended using homologous primers and the 5' and 3' ends of the transcript determined by 5' and 3' RACE. The mRNA codes for a polypeptide chain 994 amino acid residues long (coded for by 2982 nucleotides) and has a 195 bp 5' untranslated region, with a 697 bp 3' untranslated region. The scallop enzyme shows strongest amino acid similarity to the SERCA enzyme of Loligo, followed by those of Drosophila and Artemia. It resembles the vertebrate SERCA3 in that it does not possess the phospholamban binding motif and so is unlikely to be regulated by protein kinase A mediated signals.