Transfer-messenger RNA-SmpB protein regulates ribonuclease R turnover by promoting binding of HslUV and lon proteases

Wenxing Liang, Murray P. Deutscher

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31 Scopus citations


RNase R, an important exoribonuclease involved in degradation of structured RNA, is subject to a novel mechanism of regulation. The enzyme is extremely unstable in rapidly growing cells but becomes stabilized under conditions of stress, such as stationary phase or cold shock. RNase R instability results from acetylation which promotes binding of tmRNA-SmpB, two trans-translation factors, to its C-terminal region. Here, we examine how binding of tmRNA-SmpB leads to proteolysis of RNase R. We show that RNase R degradation is due to two proteases, HslUV and Lon. In their absence, RNase R is stable. We also show, using an in vitro system that accurately replicates the in vivo process, that tmRNA-SmpB is not essential, but it stimulates binding of the protease to the N-terminal region of RNase R and that it does so by a direct interaction between the protease and SmpB which stabilizes protease binding. Thus, a sequence of events, initiated by acetylation of a single Lys residue, results in proteolysis of RNase R in exponential phase cells. RNase R in stationary phase or in cold-shocked cells is not acetylated, and thereby remains stable. Such a regulatory mechanism, dependent on protein acetylation, has not been observed previously in bacterial cells.

Original languageEnglish (US)
Pages (from-to)33472-33479
Number of pages8
JournalJournal of Biological Chemistry
Issue number40
StatePublished - Sep 28 2012

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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