期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1980
卷号：77
期号：2
页码：837-841
DOI：10.1073/pnas.77.2.837
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：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.
