TEDA School of Biological Sciences and Biotechnology, Nankai University, 23 Hongda Street, TEDA, Tianjin 300457, PR China.
Nucleic Acids Res. 2012 May;40(10):4530-8. doi: 10.1093/nar/gks040. Epub 2012 Jan 28.
Flagella contribute to the virulence of bacteria through chemotaxis, adhesion to and invasion of host surfaces. Flagellar phase variation is believed to facilitate bacterial evasion of the host immune response. In this study, the flnA gene that encodes Escherichia coli H17 flagellin was examined by whole genome sequencing and genetic deletion analysis. Unilateral flagellar phase variation has been reported in E. coli H3, H47 and H17 strains, although the mechanism for phase variation in the H17 strain has not been previously understood. Analysis of phase variants indicated that the flagellar phase variation in the H17 strain was caused by the deletion of an ∼35 kb DNA region containing the flnA gene from diverse excision sites. The presence of covalently closed extrachromosomal circular forms of this excised 35 kb region was confirmed by the two-step polymerase chain reaction. The deletion and complementation test revealed that the Int1157 integrase, a tyrosine recombinase, mediates the excision of this region. Unlike most tyrosine recombinases, Int1157 is suggested to recognize diverse sites and mediate recombination between non-homologous DNA sequences. This is the first report of non-homologous recombination mediating flagellar phase variation.
鞭毛通过趋化作用、黏附和侵袭宿主表面促进细菌的毒力。鞭毛的相位变化被认为有助于细菌逃避宿主的免疫反应。在这项研究中，通过全基因组测序和遗传缺失分析研究了编码大肠杆菌 H17 鞭毛蛋白的 flnA 基因。已经报道了大肠杆菌 H3、H47 和 H17 菌株中的单侧鞭毛相位变化，尽管以前不了解 H17 菌株中相位变化的机制。相位变体的分析表明，H17 菌株的鞭毛相位变化是由从不同切除位点缺失包含 flnA 基因的约 35kb DNA 区域引起的。通过两步聚合酶链反应证实了该切除的 35kb 区域的共价闭合的染色体外环状形式的存在。缺失和互补测试表明，整合酶 Int1157，一种酪氨酸重组酶，介导该区域的切除。与大多数酪氨酸重组酶不同，Int1157 被认为可以识别不同的位点，并介导非同源 DNA 序列之间的重组。这是报道的首次非同源重组介导鞭毛相位变化。
