Robbe-Saule Véronique, Carreira Ingrid, Kolb Annie, Norel Françoise
Unité de Génétique moléculaire and CNRS URA2172, Institut Pasteur, Paris Cedex 15, France.
J Bacteriol. 2008 Jul;190(13):4453-9. doi: 10.1128/JB.00154-08. Epub 2008 May 2.
The small regulatory protein Crl favors association of the stationary-phase sigma factor sigma(S) (RpoS) with the core enzyme polymerase and thereby increases sigma(S) activity. Crl has a major physiological impact at low levels of sigma(S). Here, we report that the Crl effects on sigma(S)-dependent gene expression, the H(2)O(2) resistance of Salmonella enterica serovar Typhimurium, and the resistance of this organism to acidic pH are greater at 28 degrees C than at 37 degrees C. Immunoblot experiments revealed a negative correlation between sigma(S) and Crl levels; the production of Crl was slightly greater at 28 degrees C than at 37 degrees C, whereas the sigma(S) levels were about twofold lower at 28 degrees C than at 37 degrees C. At both temperatures, Crl was present in excess of sigma(S), and increasing the Crl level further did not increase the H(2)O(2) resistance level of Salmonella and the expression of the sigma(S)-dependent gene katE encoding the stationary-phase catalase. In contrast, increasing the sigma(S) level rendered Salmonella more resistant to H(2)O(2) at 28 degrees C, increased the expression of katE, and reduced the magnitude of Crl activation. In addition, the effect of Crl on katE transcription in vitro was not dependent on temperature. These results suggest that the effect of temperature on Crl-dependent regulation of the katE gene and H(2)O(2) resistance are mediated mainly via an effect on sigma(S) levels. In addition, our results revealed that sigma(S) exerts a negative effect on the production of Crl in stationary phase when the cells contain high levels of sigma(S).
小调节蛋白Crl有利于稳定期σ因子σ(S)(RpoS)与核心酶聚合酶结合,从而提高σ(S)的活性。Crl在低水平的σ(S)时具有主要的生理影响。在此,我们报道Crl对σ(S)依赖性基因表达、肠炎沙门氏菌鼠伤寒血清型对H₂O₂的抗性以及该菌对酸性pH的抗性在28℃时比在37℃时更强。免疫印迹实验揭示了σ(S)和Crl水平之间呈负相关;Crl的产生在28℃时略高于37℃,而σ(S)水平在28℃时比在37℃时低约两倍。在两个温度下,Crl的存在量都超过σ(S),进一步提高Crl水平并不会增加沙门氏菌对H₂O₂的抗性水平以及编码稳定期过氧化氢酶的σ(S)依赖性基因katE的表达。相反,提高σ(S)水平使沙门氏菌在28℃时对H₂O₂更具抗性,增加了katE的表达,并降低了Crl激活的程度。此外,Crl对体外katE转录的影响不依赖于温度。这些结果表明,温度对Crl依赖性的katE基因调控和H₂O₂抗性的影响主要是通过对σ(S)水平的作用介导的。此外,我们的结果表明,当细胞中σ(S)水平较高时,σ(S)在稳定期对Crl的产生具有负面影响。