Smeds A, Varmanen P, Palva A
Agricultural Research Centre of Finland, Food Research Institute, Jokioinen 31600, Finland.
J Bacteriol. 1998 Dec;180(23):6148-53. doi: 10.1128/JB.180.23.6148-6153.1998.
A gene (htrA) coding for a stress-inducible HtrA-like protein from Lactobacillus helveticus CNRZ32 was cloned, sequenced, and characterized. The deduced amino acid sequence of the gene exhibited 30% identity with the HtrA protein from Escherichia coli; the putative catalytic triad and a PDZ domain that characterize the HtrA family of known bacterial serine proteases were also found in the sequence. Expression of the L. helveticus htrA gene in a variety of stress conditions was analyzed at the transcriptional level. The strongest induction, resulting in over an eightfold increase in the htrA transcription level, was found in growing CNRZ32 cells exposed to 4% (wt/vol) NaCl. Enhanced htrA mRNA expression was also seen in CNRZ32 cells after exposure to puromycin, ethanol, or heat. The reporter gene gusA was integrated in the Lactobacillus chromosome downstream of the htrA promoter by a double-crossover event which also interrupted the wild-type gene. The expression of gusA in the stress conditions tested was similar to that of htrA itself. In addition, the presence of an intact htrA gene facilitated growth under heat stress but not under salt stress.
对瑞士乳杆菌CNRZ32中编码应激诱导型类HtrA蛋白的基因（htrA）进行了克隆、测序和特性分析。该基因推导的氨基酸序列与大肠杆菌的HtrA蛋白有30%的同源性；在该序列中还发现了表征已知细菌丝氨酸蛋白酶HtrA家族的假定催化三联体和一个PDZ结构域。在转录水平分析了瑞士乳杆菌htrA基因在各种应激条件下的表达情况。在暴露于4%（重量/体积）NaCl的生长中的CNRZ32细胞中发现了最强的诱导作用，导致htrA转录水平增加了八倍以上。在暴露于嘌呤霉素、乙醇或热之后，CNRZ32细胞中也观察到htrA mRNA表达增强。通过双交换事件将报告基因gusA整合到htrA启动子下游的乳杆菌染色体中，该双交换事件同时中断了野生型基因。在测试的应激条件下，gusA的表达与htrA自身的表达相似。此外，完整htrA基因的存在促进了热应激下的生长，但在盐应激下则不然。
