Keenleyside W J, Whitfield C
Department of Microbiology, University of Guelph, Ontario, Canada.
J Bacteriol. 1995 Sep;177(18):5247-53. doi: 10.1128/jb.177.18.5247-5253.1995.
Plasmid pWQ799 is a 6.9-kb plasmid isolated from Salmonella enterica serovar Borreze. Our previous studies have shown that the plasmid contains a functional biosynthetic gene cluster for the expression of the O:54 lipopolysaccharide O-antigen of this serovar. The minimal replicon functions of pWQ799 have been defined, and a comparison with nucleotide and protein databases revealed this replicon to be virtually identical to ColE1. This is the first report of involvement of ColE1-related plasmids in O-antigen expression. The replicon of pWQ799 is predicted to encode two RNA molecules, typical of other ColE1-type plasmids. RNAII, the putative replication primer from pWQ799, shares regions of homology with RNAII from ColE1. RNA1 is an antisense regulator of DNA replication in ColE1-related plasmids. The coding region for RNAI from pWQ799 shares no homology with any other known RNAI sequence but is predicted to adopt a secondary structure characteristic of RNAI molecules. pWQ799 may therefore represent a new incompatibility group within this family. pWQ799 also possesses cer, rom, and mob determinants, and these differ minimally from those of ColE1. The plasmid is mobilizable in the presence of either the broad-host-range helper plasmid pRK2013 or the IncI1 plasmid R64drd86. Mobilization and transfer of pWQ799 to other organisms provides the first defined mechanism for lateral transfer of O-antigen biosynthesis genes in S. enterica and explains both the distribution of related plasmids and coexpression of the O:54 factor with other O-factors in different Salmonella serovars. The base composition of the pWQ799 replicon sequences gives an average percent G+C value typical of Salmonella spp. In contrast, the percent G+C value is dramatically lower with rfb0:54, consistent with the possibility that the cluster was acquired from an organism with much lower G+C composition.
质粒pWQ799是一种从肠炎沙门氏菌波雷泽血清型中分离出的6.9 kb质粒。我们之前的研究表明，该质粒包含一个功能性生物合成基因簇，用于表达该血清型的O:54脂多糖O抗原。已确定了pWQ799的最小复制子功能，与核苷酸和蛋白质数据库的比较显示该复制子与ColE1几乎完全相同。这是关于ColE1相关质粒参与O抗原表达的首次报道。预计pWQ799的复制子编码两个RNA分子，这是其他ColE1型质粒的典型特征。来自pWQ799的假定复制引物RNAII与来自ColE1的RNAII具有同源区域。RNA1是ColE1相关质粒中DNA复制的反义调节因子。来自pWQ799的RNAI编码区与任何其他已知的RNAI序列均无同源性，但预计会形成RNAI分子特有的二级结构。因此，pWQ799可能代表了该家族中的一个新的不相容群。pWQ799还具有cer、rom和mob决定簇，这些与ColE1的决定簇差异极小。在广泛宿主范围的辅助质粒pRK2013或IncI1质粒R64drd86存在的情况下，该质粒是可移动的。pWQ799向其他生物体的移动和转移为肠炎沙门氏菌中O抗原生物合成基因的横向转移提供了首个明确机制，并解释了相关质粒的分布以及不同沙门氏菌血清型中O:54因子与其他O因子的共表达。pWQ799复制子序列的碱基组成给出了沙门氏菌属典型的平均G+C百分比值。相比之下，rfb0:54的G+C百分比值显著较低，这与该基因簇是从G+C组成低得多的生物体中获得的可能性一致。
