THE NEWT RIBOZYME IS PART OF A RIBOPROTEIN COMPLEX

Strand-specific transcripts of a satellite DNA of the newts, Notophtha lmus and Triturus, are present in cells in monomeric and multimeric si zes, These transcripts undergo self-catalyzed, site-specific cleavage in vitro: the reaction requires Mg2+ and is mediated by a ''hammerhead '' domain, Transcription of the newt ribozyme appears to be performed by RNA polymerase II under the control of a proximal sequence element and a distal sequence element, In vitro, the newt ribozyme can cleave in trans an RNA substrate, suggesting that in vivo it might be involve d in RNA processing events, perhaps as a riboprotein complex, Here we show that the newt ribozyme is in fact present as a riboprotein partic le of about 12 S in the oocytes of Triturus. In addition, reconstituti on experiments and gel-shift analyses show that a complex is assembled in vitro on the monomeric ribozyme molecules, UV cross-linking studie s identify a few polypeptide species, ranging from 31 to 65 kDa, assoc iated to the newt ribozyme with different affinities, Finally, we find that an appropriate oligoribonucleotide substrate is specifically cle aved by the riboproteic activity in S-100 ovary extracts.