title: Purification and characterization of Escherichia coli RNase T.
abstract: RNase T, a nuclease thought to be involved in end-turnover of tRNA, has been purified about 4,000-fold from extracts of Escherichia coli. At this stage of purification, the enzyme was judged to be at least 95% pure based on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The native molecular weight of RNase T determined from gel filtration and sedimentation analyses is about 50,000, whereas the monomer molecular weight determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis is 25,000, suggesting that the protein is an alpha 2 dimer. Purified RNase T is extremely sensitive to inactivation by oxidation, sulfhydryl group reagents, and temperature. The ribonuclease activity against tRNA-C-C-[14C]A is optimal at pH 8-9 in the presence of 2-5 mM MgCl2 and ionic strengths of less than 50mM. Although RNase T is highly specific for intact tRNA-C-C-A as a substrate and can hydrolyze all species in a mixed population of tRNA, it is inhibited by other RNAs, such as poly(A), rRNA, 5 S RNA, and tRNA-C-C. RNase T is an exoribonuclease which initiates attack at a free 3' terminus of tRNA and releases AMP; aminoacyl-tRNA is not a substrate. The role of RNase T in the end-turnover of tRNA and its possible involvement in other aspects of RNA metabolism are discussed.
mesh_terms: D002850:Chromatography, Gel; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000201:enzymology*; D005095:Exoribonucleases / Q000302:isolation & purification*; D006868:Hydrolysis; D013439:Sulfhydryl Reagents / Q000494:pharmacology; D013696:Temperature; D014462:Ultrafiltration
chemical_list: D013439:Sulfhydryl Reagents; D005095:Exoribonucleases; C042081:exoribonuclease T