Identification of protein A-binding components in Spisula oocytes.

Components involved in sustaining meiosis arrest of oocytes were determined. Proteins that bind to protein A from meiosis-arrested and 5-HT-matured Spisula oocytes were analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Meiosis-arrested oocytes contained three doublets of proteins with estimated Mrs of 43 and 45, 38 and 40, and 21 and 23 kDa. In 5 HT-matured oocytes the 21 and 23 and 38 and 40 kDa proteins were retained; whereas the 43 and 45 kDa proteins were absent. The protein A-bound proteins did not interact with antibodies against the various subclasses of human, mouse, rat and rabbit IgG or human Fc fragment. The amino acid sequence of the N-terminus of the 43 kDa protein was determined to be NH2-VLRIGSGMXDT. Comparison of this sequence with existing database at Protein Identification Resource (R 32.0), GenBank (R 72.0), SWISS-PROT (R 22.0), and EMBL (R 31.0) showed no homology with any reported protein. The protein A-bound components from meiosis-arrested oocytes were incubated in vitro with [gamma-32P]ATP. Only the 68 kDa protein was radiophosphorylated. This protein was not detected in 5-HT-matured oocytes. The disappearance of the 43, 45, and 68 kDa proteins in 5-HT-matured oocytes suggests that these components may be involved in sustaining meiosis meiosis. A unique property of these proteins is that they interact with protein A and are distinctly different from immunoglobulin.