Galán J E, Curtiss R
Department of Biology, Washington University, St. Louis, Missouri 63130.
Infect Immun. 1990 Jun;58(6):1879-85. doi: 10.1128/iai.58.6.1879-1885.1990.
The ability to enter intestinal epithelial cells is an essential virulence factor of salmonellae. We have previously cloned a group of genes (invA, B, C, and D) that allow S. typhimurium to penetrate tissue culture cells (J. E. Galán and R. Curtiss III, Proc. Natl. Acad. Sci. USA 86:6383-6387, 1989). Transcriptional and translational cat and phoA fusions to invA (the proximal gene in the invABC operon) were constructed, and their expression was studied by measuring the levels of alkaline phosphatase or chloramphenicol acetyltransferase activity in mutants grown under different conditions. It was found that when strains containing the fusions were grown on media with high osmolarity, a condition known to increase DNA superhelicity, the level of invA transcription was approximately eightfold higher than that in strains grown on media with low osmolarity. The osmoinducibility of invA was independent of ompR, which controls the osmoinducibility of other genes. Strains grown in high-osmolarity media in the presence of subinhibitory concentrations of gyrase inhibitors (novobiocin or coumermycin A1), which reduce the level of DNA supercoiling, showed reduced expression of invA. Nevertheless, invA was poorly expressed in topA mutants of S. typhimurium, which have increased DNA superhelicity. In all cases, the differential expression of the invasion genes was correlated with the ability of S. typhimurium to penetrate tissue culture cells. These results taken together indicate that expression of S. typhimurium invasion genes is affected by changes in DNA supercoiling and suggest that this may represent a way in which this organism regulates the expression of these genes.
进入肠道上皮细胞的能力是沙门氏菌的一种重要毒力因子。我们之前克隆了一组基因（invA、B、C和D），这些基因可使鼠伤寒沙门氏菌穿透组织培养细胞（J. E. 加兰和R. 柯蒂斯三世，《美国国家科学院院刊》86:6383 - 6387, 1989）。构建了与invA（invABC操纵子中的近端基因）的转录和翻译融合的cat和phoA，并通过测量在不同条件下生长的突变体中碱性磷酸酶或氯霉素乙酰转移酶活性水平来研究它们的表达。结果发现，当含有融合基因的菌株在高渗透压培养基上生长时（已知这种条件会增加DNA超螺旋度），invA转录水平比在低渗透压培养基上生长的菌株高约八倍。invA的渗透诱导性独立于控制其他基因渗透诱导性的ompR。在存在亚抑制浓度的促旋酶抑制剂（新生霉素或香豆霉素A1）的情况下于高渗透压培养基中生长的菌株，其DNA超螺旋水平降低，invA的表达也降低。然而，invA在DNA超螺旋度增加的鼠伤寒沙门氏菌topA突变体中表达不佳。在所有情况下，侵袭基因的差异表达与鼠伤寒沙门氏菌穿透组织培养细胞的能力相关。综合这些结果表明，鼠伤寒沙门氏菌侵袭基因的表达受DNA超螺旋变化的影响，并表明这可能是该生物体调节这些基因表达的一种方式。
