Department of Veterinary Disease Biology, Faculty of Life Sciences, University of Copenhagen, Stigbøjlen 4, DK-1870 Frederiksberg C, Denmark.
Departamento de Quimica, Bioquimica y Biologia Molecular, Universidad Cardenal Herrera-CEU, Moncada, Valencia 46113, Spain.
Microbiology (Reading). 2011 Mar;157(Pt 3):677-684. doi: 10.1099/mic.0.043794-0. Epub 2010 Dec 23.
The SOS response is governed by the transcriptional regulator LexA and is elicited in many bacterial species in response to DNA damaging conditions. Induction of the SOS response is mediated by autocleavage of the LexA repressor resulting in a C-terminal dimerization domain (CTD) and an N-terminal DNA-binding domain (NTD) known to retain some DNA-binding activity. The proteases responsible for degrading the LexA domains have been identified in Escherichia coli as ClpXP and Lon. Here, we show that in the human and animal pathogen Staphylococcus aureus, the ClpXP and ClpCP proteases contribute to degradation of the NTD and to a lesser degree the CTD. In the absence of the proteolytic subunit, ClpP, or one or both of the Clp ATPases, ClpX and ClpC, the LexA domains were stabilized after autocleavage. Production of a stabilized variant of the NTD interfered with mitomycin-mediated induction of sosA expression while leaving lexA unaffected, and also significantly reduced SOS-induced mutagenesis. Our results show that sequential proteolysis of LexA is conserved in S. aureus and that the NTD may differentially regulate a subset of genes in the SOS regulon.
SOS 反应受转录调节因子 LexA 控制，在许多细菌物种中，当 DNA 受到损伤时，会引发 SOS 反应。SOS 反应的诱导是通过 LexA 阻遏物的自我切割介导的，导致 C 端二聚化结构域 (CTD) 和 N 端 DNA 结合结构域 (NTD)。已知 NTD 保留一些 DNA 结合活性。在大肠杆菌中，负责降解 LexA 结构域的蛋白酶已被鉴定为 ClpXP 和 Lon。在这里，我们表明在人类和动物病原体金黄色葡萄球菌中，ClpXP 和 ClpCP 蛋白酶有助于 NTD 的降解，并在较小程度上有助于 CTD 的降解。在缺乏蛋白酶亚基 ClpP 或一个或两个 Clp ATPase（ClpX 和 ClpC）的情况下，LexA 结构域在自我切割后稳定。NTD 稳定变体的产生干扰了丝裂霉素诱导的 sosA 表达，而对 lexA 没有影响，也显著降低了 SOS 诱导的突变。我们的研究结果表明，LexA 的顺序蛋白水解在金黄色葡萄球菌中是保守的，并且 NTD 可能在 SOS 调控基因中差异调节一组基因。
