Li L Y, Shoemaker N B, Wang G R, Cole S P, Hashimoto M K, Wang J, Salyers A A
Department of Microbiology, University of Illinois, Urbana 61801, USA.
J Bacteriol. 1995 Jul;177(14):3940-5. doi: 10.1128/jb.177.14.3940-3945.1995.
Bacteroides conjugative transposons can act in trans to excise, circularize, and transfer unlinked integrated elements called NBUs (for nonreplicating Bacteroides units). Previously, we localized and sequenced the mobilization region of one NBU, NBU1, and showed that this mobilization region was recognized by the IncP plasmids RP4 and R751, as well as by the Bacteroides conjugative transposons. We report here that the single mobilization protein carried by NBU1 appears to be a bifunctional protein that binds to the oriT region and catalyzes the nicking reaction that initiates the transfer process. We have also localized and sequenced the mobilization region of a second NBU, NBU2. The NBU2 mobilization region was 86 to 90% identical at the DNA sequence to the oriT-mob region of NBU1. The high sequence similarity between NBU1 and NBU2 ended abruptly after the stop codon of the mob gene and about 1 kbp upstream of the oriT region, indicating that the oriT-mob regions of NBU1 and NBU2 may be on some sort of cassette. A region on NBU1 and NBU2 which lies immediately upstream of the oriT region had 66% sequence identity to a region upstream of the oriT region on a mobilizable transposon, Tn4399, an element that had previously appeared to be completely unrelated to the NBUs.
拟杆菌属接合转座子可通过反式作用切除、环化并转移未连锁的整合元件，即所谓的NBU（非复制性拟杆菌单位）。此前，我们对一个NBU（NBU1）的动员区域进行了定位和测序，结果表明该动员区域可被IncP质粒RP4和R751以及拟杆菌属接合转座子识别。我们在此报告，NBU1携带的单一动员蛋白似乎是一种双功能蛋白，它可与oriT区域结合并催化引发转移过程的切口反应。我们还对第二个NBU（NBU2）的动员区域进行了定位和测序。NBU2的动员区域在DNA序列上与NBU1的oriT - mob区域有86%至90%的同一性。NBU1和NBU2之间的高序列相似性在mob基因的终止密码子之后以及oriT区域上游约1 kbp处突然终止，这表明NBU1和NBU2的oriT - mob区域可能存在于某种盒式结构上。NBU1和NBU2上oriT区域紧邻上游的一个区域与可移动转座子Tn4399上oriT区域上游的一个区域有66%的序列同一性，Tn4399是一种之前似乎与NBU完全无关的元件。
