Seegers J F, Bron S, Franke C M, Venema G, Kiewiet R
Department of Genetics, Centre of Biological Sciences, Haren, The Netherlands.
Microbiology (Reading). 1994 Jun;140 ( Pt 6):1291-300. doi: 10.1099/00221287-140-6-1291.
DNA sequence analysis and Southern hybridizations, together with complementation experiments, were used to study relationships between lactococcal plasmid replicons. pWVO2, pWVO4 and pWVO5, which co-exist in Lactococcus lactis subsp. cremoris Wg2, and pIL7 (isolated from another strain) all contained a functional replication region which appeared to be very similar to that of some known lactococcal plasmids. They contain a gene encoding a highly conserved RepB protein (60-80% amino acid identity between pWVO2, pWVO4 and pWVO5), which is essential for replication. When supplied in trans, repB of pWVO2 complemented a repB deficiency of pWVO5. Upstream of the repB gene, all these plasmids contain a strongly conserved region including a 22 bp sequence tandemly repeated three-and-a-half times, and an A/T-rich region. The similarity with pWVO2, which is known to replicate via a theta mechanism, suggests that all plasmids of this family are capable of theta replication. Southern hybridizations revealed that many lactococcal strains contain plasmids of this family.
DNA序列分析、Southern杂交以及互补实验被用于研究乳球菌质粒复制子之间的关系。共存于乳酸乳球菌乳脂亚种Wg2中的pWVO2、pWVO4和pWVO5，以及pIL7（从另一菌株中分离得到）都含有一个功能性复制区域，该区域似乎与一些已知的乳球菌质粒非常相似。它们含有一个编码高度保守的RepB蛋白的基因（pWVO2、pWVO4和pWVO5之间氨基酸同一性为60 - 80%），这对复制至关重要。当以反式提供时，pWVO2的repB补充了pWVO5的repB缺陷。在repB基因上游，所有这些质粒都含有一个高度保守的区域，包括一个22 bp序列串联重复三次半，以及一个富含A/T的区域。与已知通过θ机制复制的pWVO2的相似性表明，该家族的所有质粒都能够进行θ复制。Southern杂交显示，许多乳球菌菌株都含有该家族的质粒。
