Showing papers by "Murray P. Deutscher published in 1980"
TL;DR: Compared 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.
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.
55 citations
TL;DR: Threonyl-tRNA synthetase was purified approximately 500-fold from a high-speed supernatant fraction of rat liver and appears to be an alpha 2 dimer, while preliminary carbohydrate analyses suggested that the enzyme is a glycoprotein.
Abstract: Threonyl-tRNA synthetase was purified approximately 500-fold from a high-speed supernatant fraction of rat liver. The purified enzyme was estimated to be > 95% pure from acrylamide gel electrophoresis under denaturing and nondenaturing conditions. Based on a native molecular weight from sedimentation equilibrium of 154000 and a subunit molecular weight of 85000 obtained bo sodium dodecyl sulfate gel electrophoresis, the protein appears to be an alpha 2 dimer. The alpha 2 structure was also supported by cross-linking studies of the native enzyme. The purified protein has an S20,w of 7.2 and an isoelectric point of 6.4. Amino acid analyses revealed no unusual features, but attempts at automated sequence analyses suggested that both amino termini are blocked. Preliminary carbohydrate analyses suggested that the enzyme is a glycoprotein. Antibodies were raised against the purified protein which could inactivate and precipitate threonyl-tRNA synthetase.
36 citations