POLYADENYLATION-MEDIATED TRANSLATIONAL REGULATION OF MATERNAL P450(11-BETA) MESSENGER-RNA IN FROG OOCYTES

Northern blot analysis of bullfrog tissues using a cDNA probe of cytoc hrome P450(11 beta) showed that a large amount of message was present in the ovary as well as in the adrenal tissue. Two kinds of mRNA of di fferent sizes were found in the ovary. Sequence determination of the t wo cDNAs and analysis by reverse-transcription polymerase chain reacti on indicated that the protein encoded by the larger mRNA was identical to the adrenal enzyme, while the protein encoded by the smaller had a truncated sequence lacking an extension peptide necessary for the pro tein transport to the mitochondria, The mRNAs were present in the oocy tes but not in the follicular cells, and their content in an oocyte va ried little during its maturation. Immunoblot analyses of the mitochon drial fraction of oocytes failed to demonstrate the presence of P450(1 1 beta) protein, In contrast the eggs were found to contain a large am ount of enzymatically active protein. Interestingly the mRNA has a cis -element called cytoplasmic polyadenylation element at its 3' untransl ated region. When poly(A) tails of the message prepared from eggs and oocytes were examined by RNase H digestion or reverse-transcription po lymerase chain reaction, those of eggs were about 150 nucleotides long er than those of oocytes. These results suggest that translation of th e message is stimulated during the oocyte maturation as a result of en hanced polyadenylation at its 3'-end. Finally a finding is presented t hat progesterone was converted to 11 beta-hydroxyprogesterone by the f rog P450(11 beta), implying that the enzyme expressed in eggs may cont rol a level of progesterone which is needed to initiate the oocyte mat uration.