A single mRNA encodes multiple copies of the egg peptide speract

Abstract

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. Stronglyocentrotus 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.(ABSTRACT TRUNCATED AT 250 WORDS)