School of Dentistry, Indiana University, Indianapolis, IN 46202, USA.
Plasmid. 2010 May;63(3):136-42. doi: 10.1016/j.plasmid.2010.02.001. Epub 2010 Feb 6.
Conjugal transfer of plasmid DNA initiates and terminates at a specific non-coding site called the origin of transfer (oriT). Previous analysis of conjugative plasmid pVT745 from Aggregatibacter actinomycetemcomitans suggested that oriT was located adjacent to the operon responsible for initiation of ssDNA transfer. The location of oriT was confirmed by assaying both subclones of the region as well as a pVT745 deletion derivative for mobilization. The precise DNA nick site (nic) and polarity of DNA transfer were identified by use of interrupted mating assays, a technique originally used for the mapping of bacterial chromosomes. Nucleotide sequence analysis revealed that the pVT745-specific nick region was similar to the consensus nick sequence of the IncP family albeit the actual cleavage site differed. Functionality of nic was confirmed by point mutations.
质粒 DNA 的共轭转移在一个称为转移起始点（oriT）的特定非编码位点起始和终止。先前对源自伴放线放线杆菌的共轭质粒 pVT745 的分析表明，oriT 位于负责 ssDNA 转移起始的操纵子附近。oriT 的位置通过对该区域的两个亚克隆以及 pVT745 缺失衍生物进行移动性测定来确认。使用中断交配测定（最初用于细菌染色体作图的技术）确定了精确的 DNA 切口位点（nic）和 DNA 转移的极性。核苷酸序列分析表明，pVT745 特异性切口区域与 IncP 家族的共识切口序列相似，尽管实际的切割位点不同。通过点突变证实了 nic 的功能。
