REGULATED POLYADENYLATION OF CLAM MATERNAL MESSENGER-RNAS IN-VITRO

During meiotic maturation of Spisula oocytes, maternal mRNAs undergo c hanges in translation and in the length of their poly(A) tails. In gen eral, those mRNAs that are translationally activated, i.e., unmasked, become polyadenylated, while deactivated mRNAs lose their poly(A) tail s. The activated class of mRNAs encode ribonucleotide reductase, cycli ns A and B and histone H3, while the proteins that stop being made inc lude tubulin and actin. Previously, we demonstrated that mRNA-specific unmasking can be brought about in vitro by preventing the interaction of protein(s) with central portions of the 3' noncoding regions (mask ing regions) of ribonucleotide reductase and cyclin A mRNAs. In this r eport, we show that clam egg extracts are capable of sequence-specific polyadenylation of added RNAs since the 3' untranslated regions (UTRs ) of ribonucleotide reductase and histone H3 mRNAs are polyadenylated, while that of actin mRNA is not. In contrast, oocyte extracts, as in vivo, are essentially devoid of polyadenylation activity. We present a n initial characterisation of the cis-acting sequences in the 3' UTR o f ribonucleotide reductase mRNA required for polyadenylation. The resu lts suggest that the sequences for cytoplasmic polyadenylation are mor e complex and extensive than those determined in vertebrates and that they may partly overlap with the masking regions. (C) 1993 Wiley-Liss, Inc.