title: Escherichia coli RNase M is a multiply altered form of RNase I.
abstract: RNase M, an enzyme previously purified to homogeneity from Escherichia coli, was suggested to be the RNase responsible for mRNA degradation in this bacterium. Although related to the endoribonuclease, RNase I, its distinct properties led to the conclusion that RNase M was a second, low molecular mass, broad specificity endoribonuclease present in E. coli. However, based on sequence analysis, southern hybridization, and enzyme activity, we show that RNase M is, in fact, a multiply altered form of RNase I. In addition to three amino acid substitutions that confer the properties of RNase M on the mutated RNase I, the protein is synthesized from an rna gene that contains a UGA nonsense codon at position 5, apparently as a result of a low level of readthrough. We also suggest that RNase M is just one of several previously described endoribonuclease activities that are actually manifestations of RNase I.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Miami School of Medicine, Florida 33101-6129, USA.
authors.forename: P R
authors.initials: PR
authors.lastname: Subbarayan
authors.forename: M P
authors.initials: MP
authors.lastname: Deutscher
mesh_terms: D004722:Endoribonucleases / Q000235:genetics* / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology*; D005798:Genes, Bacterial; D009154:Mutation; D010449:Peptide Mapping; D012259:Ribonuclease, Pancreatic / Q000235:genetics* / Q000378:metabolism; D017422:Sequence Analysis, DNA
chemical_list: D004722:Endoribonucleases; C022538:ribonuclease M; D012259:Ribonuclease, Pancreatic