Wang Jun, Karnati Pavan K, Takacs Carter M, Kowalski Joseph C, Derbyshire Keith M
Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, New York 12201, USA.
Mol Microbiol. 2005 Oct;58(1):280-8. doi: 10.1111/j.1365-2958.2005.04824.x.
Classical conjugal DNA transfer of chromosomal DNA in bacteria requires the presence of a cis-acting site, oriT, in the chromosome. Acquisition of an oriT occurs if a conjugative plasmid integrates into the chromosome to form an Hfr donor strain, which can transfer extensive regions of chromosomal DNA. Because oriT sequences are unique, and because transfer occurs in a 5' to 3' direction, the frequency with which a particular gene is inherited by the recipient depends on the gene's location: those closest to the 3' side of oriT are transferred most efficiently. In addition, as the entire chromosome must be transferred to regenerate oriT, Hfr transconjugants never become donors. Here we describe novel aspects of a chromosomal DNA transfer system in Mycobacterium smegmatis. We demonstrate that there are multiple transfer initiations from a donor chromosome and, as a result, the inheritance of any gene is location-independent. Transfer is not contiguous; instead, multiple non-linked segments of DNA can be inherited in a recipient. However, we show that, with appropriate selection, segments of DNA at least 266 kb in length can be transferred. In further contrast to Hfr transfer, transconjugants can become donors, suggesting that the recipient chromosome contains multiple cis-acting sequences required for transfer, but lacks the trans-acting transfer functions. We exploit these observations to map a donor-determining locus in the M. smegmatis chromosome using genetic linkage analysis. Together, these studies further underline the unique nature of the M. smegmatis chromosomal transfer system.
细菌中染色体DNA的经典接合性DNA转移需要染色体中存在一个顺式作用位点oriT。如果一个接合性质粒整合到染色体中形成一个Hfr供体菌株，就会获得一个oriT，该菌株可以转移染色体DNA的大片段区域。由于oriT序列是独特的，并且转移是沿5'到3'方向进行的，受体遗传特定基因的频率取决于该基因的位置：那些最靠近oriT 3'端的基因转移效率最高。此外，由于整个染色体必须被转移才能再生oriT，Hfr转接合子永远不会成为供体。在这里，我们描述了耻垢分枝杆菌染色体DNA转移系统的新特点。我们证明，供体染色体存在多个转移起始点，因此，任何基因的遗传都与位置无关。转移不是连续的；相反，受体可以遗传多个不相连的DNA片段。然而，我们表明，通过适当的筛选，可以转移长度至少为266 kb的DNA片段。与Hfr转移进一步不同的是，转接合子可以成为供体，这表明受体染色体含有转移所需的多个顺式作用序列，但缺乏反式作用转移功能。我们利用这些观察结果，通过遗传连锁分析在耻垢分枝杆菌染色体中定位了一个供体决定位点。总之，这些研究进一步强调了耻垢分枝杆菌染色体转移系统的独特性质。
