3'-5' exoribonuclease that releases 5'-nucleoside monophosphates and is involved in maturation of structured RNAs (rRNAs, tRNAs and SsrA/tmRNA). In stationary phase, involved in the post-transcriptional regulation of ompA mRNA stability. Shortens RNA processively to di- and trinucleotides. In vitro, exhibits helicase activity, which is independent of its RNase activity. RNases 2 and R (rnb and this entry) contribute to rRNA degradation during starvation, while RNase R and PNPase (this entry and pnp) are the major contributors to quality control of rRNA during steady state growth (PubMed:21135037). Required for the expression of virulence genes in enteroinvasive strains of E.coli. Exonucleolytic cleavage in the 3'- to 5'-direction to yield nucleoside 5'-phosphates. Stimulated by the presence of a monovalent cation (PubMed:11948193). Highly unstable in exponential growth phase. This instability is due to the binding of SsrA/tmRNA and its associated protein SmpB to the C-terminal region of RNase R (PubMed:20688916). In contrast, RNase R becomes stabilized upon entry into stationary phase. The difference in stability between exponential and stationary phase is due to the acetylation of a single lysine residue (PubMed:21981926). Optimum pH is 7.5-9.5. Optimum temperature is 50 degrees Celsius. Monomer. Induced seven- to eightfold by cold shock. Induction is mainly a result of the stabilization of the rnr transcripts. Also induced at stationary phase. Acetylated at Lys-544 by PatZ during exponential growth phase. Acetylation alters RNase R structure and enhances binding of SsrA/tmRNA and SmpB, leading to instability and degradation of RNase R. Not acetylated and stable in stationary phase cells. Belongs to the RNR ribonuclease family. RNase R subfamily. Extended N-terminus.