Identification ofMultiple RNasesinXenopuslaevis Oocytes andTheir Possible RoleintRNAProcessing

A survey ofRNasesinXenopius laes'is oocytes hasbeencarried outtoidentify potential tRNA-processing enzymes inthis system. Using avariety ofspecific and nonspecific substrates, wehaveshownthat oocytes contain multiple RNaseswith various specificities. Threeactivities thatcould cleave theextraneous residues fromtheartificial tRNAprecursor, tRNA-C-['4C]U-C, togenerate asubstrate for -C-C-Aaddition bytRNAnucleotidyltransferase wereidentified. Oneofthese wasacytoplasmic exonuclease which generated predominantly tRNA-C, whereas theothertwowerenuclear endonucleases whichcleaved theprecursor to generate tRNA-N.Thepossible involvement oftheseactivities in3'tRNA processing inoocytes isdiscussed.