Agricultural Biotechnology Institute, National Agricultural Research and Innovation Centre, 4. Szent-Györgyi Albert str., Gödöllő, Hungary.
Sci Rep. 2017 Sep 6;7(1):10595. doi: 10.1038/s41598-017-11097-0.
Dissemination of multiresistance has been accelerating among pathogenic bacteria in recent decades. The broad host-range conjugative plasmids of the IncA/C family are effective vehicles of resistance determinants in Gram-negative bacteria. Although more than 150 family members have been sequenced to date, their conjugation system and other functions encoded by the conserved plasmid backbone have been poorly characterized. The key cis-acting locus, the origin of transfer (oriT), has not yet been unambiguously identified. We present evidence that IncA/C plasmids have a single oriT locus immediately upstream of the mobI gene encoding an indispensable transfer factor. The fully active oriT spans ca. 150-bp AT-rich region overlapping the promoters of mobI and contains multiple inverted and direct repeats. Within this region, the core domain of oriT with reduced but detectable transfer activity was confined to a 70-bp segment containing two inverted repeats and one copy of a 14-bp direct repeat. In addition to oriT, a second locus consisting of a 14-bp imperfect inverted repeat was also identified, which mimicked the function of oriT but which was found to be a recombination site. Recombination between two identical copies of these sites is RecA-independent, requires a plasmid-encoded recombinase and resembles the functioning of dimer-resolution systems.
近几十年来，病原菌中的多耐药性传播一直在加速。IncA/C 家族的广泛宿主范围可移动质粒是革兰氏阴性菌中耐药决定因素的有效载体。尽管迄今为止已经测序了超过 150 个家族成员，但它们的转移系统和其他由保守质粒骨架编码的功能仍未得到充分描述。关键的顺式作用位点，即转移起始点（oriT），尚未明确鉴定。我们提供的证据表明，IncA/C 质粒在编码必需转移因子的 mobI 基因的上游有一个单一的 oriT 位点。完全活跃的 oriT 跨越约 150-bp 的富含 AT 的区域，与 mobI 和包含多个反向和正向重复的启动子重叠。在该区域内，oriT 的核心域具有降低但可检测的转移活性，局限于包含两个反向重复和一个 14-bp 正向重复的 70-bp 片段。除了 oriT，还鉴定了第二个由 14-bp 不完整反向重复组成的位点，该位点模拟了 oriT 的功能，但被发现是一个重组位点。这些位点的两个相同拷贝之间的重组是 RecA 非依赖性的，需要一个质粒编码的重组酶，并且类似于二聚体分辨率系统的功能。
