title: Apparent involvement of ribonuclease D in the 3' processing of tRNA precursors.
abstract: Escherichia coli RNase D and RNase II have been purified to homogeneity and compared for their ability to remove extra nucleotides following the -C-C-A sequence in tRNA precursors. RNase D and RNase II are single-chain proteins with molecular weights of 38,000 and 78,000, respectively. Both enzymes require a divalent cation for activity on tRNA precursors, but, in addition, RNase II is stimulated by monovalent cations. RNase D specifically removes mononucleotide residues from a mixture of tRNA precursors to generate amino acid acceptor activity for essentially all amino acids. Although RNase II can also remove precursor-specific residues, no amino acid acceptor activity is recovered. Similarly, RNase D action on the E. coli tRNATyr precursor is limited, whereas RNase II causes extensive degradation. In contrast to the processive mode of hydrolysis by RNase II, RNase D removes nucleotides randomly and slows down greatly at the -C-C-A sequence, thereby allowing the tRNA to be aminoacylated and protected from further degradation. These results suggest that RNase D is the 3'-processing nuclease in vivo and that RNase II is a nonspecific degradative enzyme. The importance of RNA conformation for correct processing is also discussed.
mesh_terms: D004926:Escherichia coli / Q000201:enzymology* / Q000378:metabolism; D009694:Nucleic Acid Precursors / Q000378:metabolism*; D012329:RNA, Bacterial / Q000378:metabolism; D012343:RNA, Transfer / Q000378:metabolism*; D012260:Ribonucleases / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D009694:Nucleic Acid Precursors; D012329:RNA, Bacterial; D012343:RNA, Transfer; D012260:Ribonucleases