Rubin E J, Lin W, Mekalanos J J, Waldor M K
Department of Microbiology and Molecular Genetics and the Shipley Institute, Harvard Medical School, Boston, MA 02111, USA.
Mol Microbiol. 1998 Jun;28(6):1247-54. doi: 10.1046/j.1365-2958.1998.00889.x.
We identified a 4.7kb cryptic plasmid in all ctxAB+ Vibrio cholerae strains we tested. An isolate of the V. cholerae classical biotype strain 0395 that harbours the cryptic plasmid at high copy number was found. Hybridization analysis demonstrated that sequences highly related or identical to this plasmid exist in all toxigenic strains of V. cholerae but were notably absent in all non-toxigenic environmental isolates that lacked the genes for toxin-co-regulated pili and the filamentous CTX prophage. Accordingly, we have named the cryptic plasmid pTLC for toxin-linked cryptic. The complete nucleotide sequence of pTLC from the high-copy-number isolate was determined. The largest open reading frame in the plasmid is predicted to encode a protein similar to the replication initiation protein (pII) of Escherichia coli F-specific filamentous phages. The nucleotide sequence of pTLC also facilitated the structural characterization of the DNA homologous to pTLC in other strains of V. cholerae. pTLC-related DNA exists in these strains as both low-copy-number, covalently closed circular DNA and tandemly duplicated, chromosomally integrated DNA. Remarkably, the chromosomally integrated form of pTLC is adjacent to the CTX prophage. The strain distribution, chromosomal location and DNA sequence of pTLC suggests that it may be a genetic element that plays some role in the biology of CTXphi, perhaps facilitating either its acquisition or its replication.
在我们检测的所有ctxAB+霍乱弧菌菌株中，我们鉴定出了一个4.7kb的隐蔽质粒。发现了一株霍乱弧菌古典生物型菌株0395的分离株，该菌株以高拷贝数携带隐蔽质粒。杂交分析表明，与该质粒高度相关或相同的序列存在于所有产毒霍乱弧菌菌株中，但在所有缺乏毒素共调控菌毛基因和丝状CTX前噬菌体的非产毒环境分离株中明显不存在。因此，我们将该隐蔽质粒命名为pTLC，即毒素相关隐蔽质粒。测定了来自高拷贝数分离株的pTLC的完整核苷酸序列。该质粒中最大的开放阅读框预计编码一种类似于大肠杆菌F特异性丝状噬菌体复制起始蛋白（pII）的蛋白质。pTLC的核苷酸序列也有助于对其他霍乱弧菌菌株中与pTLC同源的DNA进行结构表征。pTLC相关DNA在这些菌株中以低拷贝数的共价闭合环状DNA和串联重复的染色体整合DNA两种形式存在。值得注意的是，pTLC的染色体整合形式与CTX前噬菌体相邻。pTLC的菌株分布、染色体定位和DNA序列表明，它可能是一种在CTXphi生物学中发挥某种作用的遗传元件，可能有助于其获得或复制。
