EVIDENCE FOR VITELLIN MATURATION WITHIN OOCYTES OF PERINEREIS-CULTRIFERA (POLYCHAETE ANNELID)

The relationship between the five native forms of vitellin (V1-V5) previously identified in Perinereis cultrifera oocytes was studied by following the distribution of [3H]leucine between these vitellin forms after in vivo injection of the amino acid in young and submature females. By native polyacrylamide gel electrophoresis and fluorography, the highest molecular weight form of vitellin (V1, 530,000) was first (one day incubation period) detected as being radioactive while for long incubation periods (3 to 14 days) a progressive shift in labelling was observed from V1 into the smaller forms of vitellin (V2, 500,000; V3, 470,000 V4, 430,000 and V5, 390,000). During the increasing incubation periods, a progressive shift in labelling from a single high molecular weight polypeptide (P1, 176,000) into lower molecular weight fragments characteristic of the mature vitellin form V5 was found when the vitellin fractions obtained by immunoprecipitation were analysed by sodium dodecyl sulfate polyacrylamide gel electrophoresis and fluorography. These results confirm the hypothesis of a precursor-product relationship between V1 and V5 via three intermediate forms (V2 to V4) and strongly suggest that the conversion process within the oocyte involves progressive proteolytic cleavages of a single precursor component, or polypeptide subunit of V1, into those that make up V5, the mature form of vitellin.