Structure of cDNA Coding for Rat Platelet Phospholipase A21

Three cDNA clones coding for rat platelet phospholipase A2 and a homologous protein were isolated from a rat megakaryocyte cDNA library and sequenced. One (prPLA2-1) carries a 708 nucleotide long insert. The others (prPLA2-2 and -3) differ from clone 1 in three nucleotides and have a 748 nucleotide long insert. All contain a single open reading frame which encodes a 146 amino acid long polypeptide. Based on the deduced amino acid sequence, we concluded that prPLA2-1 encodes rat platelet phospholipase A2. prPLA2-2 and -3 most probably encode a protein homologous to phospholipase A2 with two amino acid replacements. A typical signal peptide sequence (21 amino acid long), located at the NH2 termini of the deduced structure, was immediately followed by a polypeptide which corresponds to the mature enzyme, suggesting that the rat platelet enzyme is not expressed as a proenzyme form. Northern blot analysis showed a single transcript, which is 900 to 1,100 nucleotides long, in the poly(A)+RNA fractions of rat megakaryocytes, bone marrow cells, peritoneal cells of caseinate-treated rats, and spleen cells.