Department of Microbiology and Immunology, Brody School of Medicine, East Carolina University, Greenville, North Carolina 27834, USA.
J Bacteriol. 2010 Sep;192(18):4643-50. doi: 10.1128/JB.00317-10. Epub 2010 Jul 16.
Bacteroides are Gram-negative anaerobes indigenous to the intestinal tract of humans, and they are important opportunistic pathogens. Mobile genetic elements, such as conjugative transposons (CTns), have contributed to an increase in antibiotic resistance in these organisms. CTns are self-transmissible elements that belong to the superfamily of integrative and conjugative elements (ICEs). CTn341 is 52 kb; it encodes tetracycline resistance and its transfer is induced by tetracycline. The mobilization region of CTn341 was shown to be comprised of a three-gene operon, mobABC, and the transfer origin, oriT. The three genes code for a nicking accessory protein, a relaxase, and a VirD4-like coupling protein, respectively. The Mob proteins were predicted to mediate the formation of the relaxosome complex, nick DNA at the oriT, and shuttle the DNA/protein complex to the mating-pore apparatus. The results of mutational studies indicated that the three genes are required for maximal transfer of CTn341. Mob gene transcription was induced by tetracycline, and this regulation was mediated through the two-component regulatory system, RteAB. The oriT region of CTn341 was located within 100 bp of mobA, and a putative Bacteroides consensus nicking site was observed within this region. Mutation of the putative nick site resulted in a loss of transfer. This study demonstrated a role of the mobilization region for transfer of Bacteroides CTns and that tetracycline induction occurs for the mob gene operon, as for the tra gene operon(s), as shown previously.
拟杆菌是革兰氏阴性厌氧菌，天然存在于人类的肠道中，它们是重要的机会性病原体。移动遗传元件，如可移动转座子（CTns），导致这些生物体对抗生素的耐药性增加。CTns 是自我可转移的元素，属于整合和共轭元件（ICEs）的超家族。CTn341 长 52kb，它编码四环素耐药性，其转移由四环素诱导。CTn341 的动员区域由三个基因组成的操纵子 mobABC 和转移原点 oriT 组成。这三个基因分别编码一个缺口辅助蛋白、一个松弛酶和一个 VirD4 样连接蛋白。Mob 蛋白被预测介导松弛体复合物的形成，在 oriT 处切割 DNA，并将 DNA/蛋白质复合物转移到交配孔装置。突变研究的结果表明，三个基因是 CTn341 最大转移所必需的。Mob 基因转录受四环素诱导，这种调节是通过双组分调节系统 RteAB 介导的。CTn341 的 oriT 区域位于 mobA 内 100bp 处，在该区域观察到一个假定的拟杆菌缺口位点。假定的缺口位点突变导致转移丧失。这项研究表明，动员区域在拟杆菌 CTn 的转移中起作用，就像以前显示的那样，四环素诱导发生在 mob 基因操纵子上，而不是 tra 基因操纵子上。
