THE DEADENYLATING NUCLEASE (DAN) IS INVOLVED IN POLY(A) TAIL REMOVAL DURING THE MEIOTIC MATURATION OF XENOPUS OOCYTES

Exonucleolytic degradation of the poly(A) tail is often the first step in the decay of eukaryotic mRNAs and is also used to silence certain maternal mRNAs translationally during oocyte maturation and early embr yonic development. We previously described the purification of a poly( A)-specific 3'-exoribonuclease (deadenylating nuclease, DAN) from mamm alian tissue. Here, the isolation and functional characterization of c DNA clones encoding human DAN is reported. Recombinant DAN overexpress ed in Escherichia coli has properties similar to those of the authenti c protein. The amino acid sequence of DAN shows homology to the RNase D family of 3'-exonucleases. DAN appears to be localized in both the n ucleus and the cytoplasm. It is not stably associated with polysomes o r ribosomal subunits. Xenopus oocytes contain nuclear and cytoplasmic DAN isoforms, both of which are closely related to the human DAN, Anti -DAN antibody microinjected into oocytes inhibits default deadenylatio n during progesterone-induced maturation. Ectopic expression of human DAN in enucleated oocytes rescues maturation-specific deadenylation, i ndicating that amphibian and mammalian DANs are functionally equivalen t.