A SINGLE MESSENGER-RNA ENCODES MULTIPLE COPIES OF THE EGG PEPTIDE SPERACT

A complementary DNA clone (2.3 kb) that encodes the egg peptide speract (Gly-Phe-Asp-Leu-Asn-Gly-Gly-Gly-Val-Gly) has been isolated from an ovary cDNA library of the sea urchin Stron-gylocentrotus purpuratus. The DNA sequence predicts an open reading frame of 296 amino acids. The likely site of initiation, however, is a downstream in-frame translation initiation codon that would result in a polypeptide of 260 amino acids containing 10 decapeptides, each separated by a single lysine residue. Four of the peptides are speract, and six have the predicted structures of Gly-Phe-Ala-Leu-Gly-Gly-Gly-Gly-Val-Gly (occurs twice), Gly-Phe-Asn-Leu-Asn-Gly-Gly-Gly-Val-Gly, Gly-Phe-Ser-Leu-Thr-Gly-Gly-Gly-Val-Gly, Gly-Thr-Met-Pro-Thr-Gly-Ala-Gly-Val-Asp, and Ile-Asp-His-Asp-Thr-Leu-Ala-Ser-Val-Ser. The isolated cDNA insert hybridized to two species of ovarian mRNA (1.2 and 2.3 kb) obtained from species known to produce speract or speract-like peptides, but failed to hybridize to RNA from other species. Subsequently, a second ovarian cDNA clone (1.2 kb) was isolated and sequenced; this clone contained two additional potential decapeptides: Ser-Phe-Asp-Leu-Asn-Gly-Gly-Gly-Val-Gly and Ser-Thr-Met-Pro-Thr-Gly-Ala-Gly-Val-Asp. The various speract and speract-like peptides found in egg-conditioned media, therefore, reflect, in part, variable structures within a single copy of mRNA. The peptides are likely processed by a combination of trypsin and carboxypeptidase B activity; although the peptides containing a Gly-Gly-Gly-Val-Gly carboxyl-terminal sequence are known to possess sperm respiration-stimulating activity, the function, if any, of the other potential peptides remains to be determined. © 1990, American Chemical Society. All rights reserved.