Posttranscriptional osmotic regulation of the sigma(s) subunit of RNA polymerase in Escherichia coli

Abstract

The s subunit of RNA polymerase (encoded by the rpoS gene) is a master regulator in a complex regulatory network that governs the expression of many stationary-phase-induced and osmotically regulated genes in Escherichia coli. rpoS expression is itself osmotically regulated by a mechanism that operates at the posttranscriptional level. Cells growing at high osmolarity already exhibit increased levels of s during the exponential phase of growth. Osmotic induction of rpoS can be triggered by addition of NaCl or sucrose and is alleviated by glycine betaine. Stimulation of rpoS translation and a change in the half-life of s from 3 to 50 min both contribute to osmotic induction. Experiments with lacZ fusions inserted at different positions within the rpoS gene indicate that an element required for s degradation is encoded between nucleotides 379 and 742 of the rpoS coding sequence.Like most single-cell organisms, bacteria must be able to cope with extreme fluctuations in the composition and physical parameters of their environments. One of these parameters is the osmolarity of the surrounding medium. When Escherichia coli cells experience a shift to high osmolarity, influx of potassium ions and synthesis of glutamate are strongly stimulated. This rapid response is followed by uptake from the medium and/or synthesis of compatible solutes and osmoprotectants like glycine betaine, proline, or trehalose (for a review, see reference 5). In parallel, the induction of numerous proteins can be observed by two-dimensional O'Farrell gel electrophoresis (4, 14). Several corresponding genes have been identified, for instance, by isolating hyperosmotically inducible lacZ or phoA gene fusions (1,3,6,(8)(9)(10)35).With respect to the regulatory mechanisms involved, two systems have been studied in detail. One is the proU operon, which encodes a glycine betaine uptake system (for a recent review, see reference 24), whereas the other is the ompF/ompC porin system, which is controlled by a typical two-component regulatory system consisting of the membrane-bound sensory histidine kinase EnvZ and the response regulatory OmpR (15,17,26,27). However, the regulatory mechanisms involved do not seem to play a general role in the osmotic regulation of many genes, and efforts to identify a global osmotic regulator have failed.By contrast, several other hyperosmotically induced genes (otsBA, treA, osmB, osmY, and bolA) are under the control of s , a sigma subunit of RNA polymerase in E. coli that is encoded by the rpoS gene (13,14,19,34). This seems to implicate s as a global regulator in the osmotic control of gene expression. In fact, this would be a second global regulatory role for s , which is usually regarded as a stationary-phasespecific sigma factor since the genes mentioned above, as well as many other s -dependent genes, are induced during entry into stationary phase (for recent reviews, see references 11, 12, and 23). Besides being growth phase regulated at the levels of transcription, translation, and s protein stability, rpoS has a...

The LysR‐like regulator LeuO in Escherichia coli is involved in the translational regulation of rpoS by affecting the expression of the small regulatory DsrA‐RNA

“…leuO is located at 1.83 min of the current physical map of the E. coli chromosome (Berlyn et al, 1996), and the location of Tn10-8 at this position was confirmed by P1 (D, E and F). The fusions used were the transcriptional r poS742 ::lacZ fusion (A and D) and the translational r poS742 ::lacZ (B and E) and r poS379 ::lacZ (C and F) fusions (Lange and Hengge-Aronis, 1994;Muffler et al, 1996a). Optical densities (circles) and specific ␤-galactosidase activities (triangles) were determined throughout the growth cycle.…”

“…by the addition of NaCl or sucrose (Muffler et al, 1996a), temperature downshift (Sledjeski et al, 1996) and during late exponential phase above a certain cell density, when cells are grown in minimal medium (Lange and Hengge-Aronis, 1994). S proteolysis is more or less strongly inhibited in response to starvation (Lange and Hengge-Aronis, 1994;Takayanagi et al, 1994), high osmolarity (Muffler et al, 1996a), heat shock (Muffler et al, 1997a) and, probably, shift to acid pH (Bearson et al, 1996). So far, osmotic upshift is the only known stress condition that at the same time stimulates rpoS translation and almost completely inhibits S degradation (Muffler et al, 1996a).…”

“…S proteolysis is more or less strongly inhibited in response to starvation (Lange and Hengge-Aronis, 1994;Takayanagi et al, 1994), high osmolarity (Muffler et al, 1996a), heat shock (Muffler et al, 1997a) and, probably, shift to acid pH (Bearson et al, 1996). So far, osmotic upshift is the only known stress condition that at the same time stimulates rpoS translation and almost completely inhibits S degradation (Muffler et al, 1996a).…”

Regulation of Activity of the Response Regulator RssB

“…RpoS는 세균 증식이 가장 활발한 대수기에서 높은 농도의 삼 투압 (Muffler et al, 1996b), 산성 pH (Bearson et al, 1996), 낮 은 온도의 생장조건과 (Sledjeski et al, 1996) 열 충격 (Muffler et al, 1997), 낮은 마그네슘 농도 (Tu et al, 2006), 산화적 스트레 스 (Loewen and Hengge-Aronis, 1994 (Gottesman, 2004). 합성된 RpoS 단백질은 정상적인 생장조건이 주어진 경우 대수기에서 많은 양이 지속적으로 생성되지만 외부 스트레스가 없는 경우 불안정하여 반감기가 3분 이내로 빠르게 분해되어 단백질 농도 가 크게 감소한다 (Lange and Hengge-Aronis, 1994;Loewen and Hengge-Aronis, 1994;Moreno et al, 2000).…”

“…세균이 빠르게 성장할 수 있는 조건에서도 RpoS 합성이 이루어지지만, 합성되는 즉시 RssB에 의해 ClpXP에 전달 되어 분해된다 (Muffler et al, 1996b;Pratt and Silhavy, 1996 (Jenal and Hengge-Aronis, 2003). RpoS는 ClpP에 의해 분해되 는데, ClpP는 serine-type protease로서 ClpA나 ClpX와 복합체 를 구성하여 단백질을 분해시킨다 (Li et al, 2010).…”