Nicholson B, Low D
Department of Pathology, University of Utah Health Sciences Center, Salt Lake City, UT 84132, USA.
Mol Microbiol. 2000 Feb;35(4):728-42. doi: 10.1046/j.1365-2958.2000.01743.x.
Plasmid-encoded fimbriae (Pef) expressed by Salmonella typhimurium mediate adhesion to mouse intestinal epithelium. The pef operon shares features with the Escherichia coli pyelonephritis-associated pilus (pap) operon, which is under methylation-dependent transcriptional regulation. These features include conserved DNA GATC box sites in the upstream regulatory region as well as homologues of the PapI and PapB regulatory proteins. Unlike Pap fimbriae, which are expressed in a variety of laboratory media, Pef fimbriae were expressed only in acidic, rich broth under standing culture conditions. Analysis of S. typhimurium grown under these conditions indicated that Pef production was regulated by a phase variation mechanism, in which the bacterial population was skewed between fimbrial expression (phase ON) and non-expression (phase OFF) states. Leucine-responsive regulatory protein (Lrp) and DNA adenine methylase (Dam) were required for pef transcription. In contrast, the histone-like protein (H-NS) and the stationary-phase sigma factor (RpoS) repressed pef transcription. Methylation of the pef GATC II site appeared to be required for pef fimbrial expression based on analysis of a GCTC II mutant that did not express Pef fimbriae. Analysis of the DNA methylation states of pef GATC sites indicated that, under acidic growth conditions, which induced Pef production, most GATC I sites were non-methylated, whereas GATC II and GATC X were predominantly methylated. The methylation protection at GATC I and GATC II was dependent upon Lrp and was modulated by PefI. Together, these results indicate that Pef production is regulated by DNA methylation, which is the first example of methylation-dependent gene regulation outside of E. coli.
鼠伤寒沙门氏菌表达的质粒编码菌毛（Pef）介导其与小鼠肠道上皮的黏附。pef操纵子与大肠杆菌肾盂肾炎相关菌毛（pap）操纵子具有共同特征，后者受甲基化依赖的转录调控。这些特征包括上游调控区域中保守的DNA GATC框位点以及PapI和PapB调控蛋白的同源物。与在多种实验室培养基中表达的Pap菌毛不同，Pef菌毛仅在静置培养条件下的酸性丰富肉汤中表达。对在这些条件下生长的鼠伤寒沙门氏菌的分析表明，Pef的产生受相变机制调控，在此机制中细菌群体在菌毛表达（开启阶段）和不表达（关闭阶段）状态之间倾斜。pef转录需要亮氨酸响应调节蛋白（Lrp）和DNA腺嘌呤甲基化酶（Dam）。相反，类组蛋白（H-NS）和稳定期σ因子（RpoS）抑制pef转录。基于对不表达Pef菌毛的GCTC II突变体的分析，pef GATC II位点的甲基化似乎是Pef菌毛表达所必需的。对pef GATC位点的DNA甲基化状态分析表明，在诱导Pef产生的酸性生长条件下，大多数GATC I位点未甲基化，而GATC II和GATC X主要甲基化。GATC I和GATC II处的甲基化保护依赖于Lrp，并受PefI调节。总之，这些结果表明Pef的产生受DNA甲基化调控，这是大肠杆菌以外甲基化依赖基因调控的首个例子。
