Hofreuter Dirk, Haas Rainer
Max von Pettenkofer Institut für Hygiene und Medizinische Mikrobiologie, Ludwig-Maximilians Universität München, Petterkoferstrasse 9A, D-80336 Munich, Germany.
J Bacteriol. 2002 May;184(10):2755-66. doi: 10.1128/JB.184.10.2755-2766.2002.
Many Helicobacter pylori isolates carry cryptic plasmids of extremely variable size. In this study we analyzed two H. pylori plasmids, pHel4 and pHel5, from H. pylori strains P8 and P29, respectively. Plasmid pHel4 consists of 10,970 bp, constituting 15 putative open reading frames (ORFs), whereas pHel5 consists of 18,291 bp, constituting 17 ORFs. The findings that both plasmids encode a conserved RepA protein and that both have an origin of replication containing an iteron place them in the group of theta plasmids. In pHel4, the products of the overlapping orf4C, orf4D, orf4E, and orf4F sequences are homologous to MobA, MobB, MobC, and MobD, encoded by colicinogenic plasmids, suggesting that pHel4 might be mobilizable. A further putative operon consists of orf4B and orf4A, the products of which are homologous to microcin C7 (MccC7) biosynthesis and secretion proteins MccB and MccC, respectively. Plasmid pHel5 carries putative genes encoding proteins with homology to an endonuclease and gene products of an H. pylori chromosomal plasticity zone. Both plasmids contain repeat sequences, such as the previously identified R2 repeat, which are considered preferred recombination sites. In pHel4, a new repeat sequence (R4 repeat), which seems to act as a hot spot for site-specific recombination, was identified. All H. pylori plasmids characterized so far have a modular structure. We suggest a model that explains the existing plasmids by insertions and deletions of genetic elements at the repeat sequences. A genetic exchange between plasmids and the bacterial chromosome, combined with plasmid mobilization, might add a novel mechanism to explain the high genetic macrodiversity within the H. pylori population.
许多幽门螺杆菌分离株携带大小极其多样的隐蔽质粒。在本研究中，我们分别分析了来自幽门螺杆菌菌株P8和P29的两个幽门螺杆菌质粒pHel4和pHel5。质粒pHel4由10,970 bp组成，包含15个推定的开放阅读框（ORF），而pHel5由18,291 bp组成，包含17个ORF。这两个质粒都编码一种保守的RepA蛋白，并且都有一个包含迭代子的复制起点，这些发现将它们归入θ质粒组。在pHel4中，重叠的orf4C、orf4D、orf4E和orf4F序列的产物与产大肠杆菌素质粒编码的MobA、MobB、MobC和MobD同源，这表明pHel4可能是可移动的。另一个推定的操纵子由orf4B和orf4A组成，其产物分别与小菌素C7（MccC7）生物合成和分泌蛋白MccB和MccC同源。质粒pHel5携带推定的基因，其编码的蛋白质与一种核酸内切酶以及幽门螺杆菌染色体可塑性区的基因产物具有同源性。这两个质粒都包含重复序列，如先前鉴定的R2重复序列，这些序列被认为是优选的重组位点。在pHel4中鉴定出一个新的重复序列（R4重复序列），它似乎是位点特异性重组热点。到目前为止所表征的所有幽门螺杆菌质粒都具有模块化结构。我们提出了一个模型，通过遗传元件在重复序列处的插入和缺失来解释现有质粒。质粒与细菌染色体之间的基因交换，再加上质粒的移动，可能会增加一种新机制来解释幽门螺杆菌群体内高度的遗传宏观多样性。
