中文摘要：

通常细菌间环型质粒在接合转移过程中，单链质粒DNA在质粒内部“oriT”接合转移起始位点发生缺刻．随后，打开的单链质粒DNA通过细胞膜N1V型分泌系统转移到受体菌中．但是，链霉菌中的接合型线型质粒带有游离3′端，5′端与末端蛋白结合，因而不能以细胞．细胞间方式转移单链缺刻DNA．报道了变铅青链霉菌线型质粒SLP2衍生的环型质粒，与SLP2一样可以高频高效接合转移，并鉴定了接合转移功能区．质粒有效的接合转移功能区包含6个共转录的基因，分别编码一个Tra样的DNA转移酶、胞壁水解酶、2个膜蛋白（可以与ATP结合蛋白相互作用）和一个功能未知的蛋白质．从Sal I R-／M-向Sal I R／M宿主转移的质粒频率下降表明，线型和环型的质粒都是以双链的形式转移的．上述研究结果表明SLP2衍生的线型质粒和环型质粒以相似的与细胞膜／胞壁功能相关的机理进行接合转移．

英文摘要：

Commonly, the interbacterial transfer of circular plasmids is initiated by nicking at an internal sequence, oriT, followed by transferring one strand as single-stranded DNA through a type IV secretion channel on cell membrane. In contrast, Streptomyces conjugative linear plasmids, containing a free 3＇-end but a protein-capped 5＇-end, can potentially undergo cell-to-cell transfer by transfer of non-nicked DNA. It was reported that circular derivatives of the Streptomyces lividans linear plasmid SLP2, as well as the parental linear plasmid itself can transfer efficiently. And the genetic requirements for such transfer was described. Efficient transfer of plasmid requires six co-transcribed SLP2 genes, encoding a Tra-like DNA translocase, cell wall hydrolase, two cell membrane proteins that interact with an ATP binding protein, and a protein of unknown function. Reduced transfer efficiency ofplasmid from Sa/I R-/M- to So/I R/M hosts argues that transfer of both the circular and linear forms of the plasmid involves double-stranded DNA. These results suggest that conjugal transfer occurs by a similar mechanism for SLP2-derived linear and circular plasmids, and cellular membrane/wall functions in the transfer process.