Parker Christopher, Meyer Richard J
Section of Molecular Genetics and Microbiology and Institute for Cellular and Molecular Biology, University of Texas at Austin, Austin, TX 78712, USA.
Mol Microbiol. 2007 Oct;66(1):252-61. doi: 10.1111/j.1365-2958.2007.05925.x.
The relaxase of the plasmid R1162 is a large protein essential for conjugative transfer and containing two different and physically separate catalytic activities. The N-terminal half cleaves one of the DNA strands at the origin of transfer (oriT) and becomes covalently linked to the 5' terminal phosphate; the C-terminal half is a primase essential for initiation of plasmid vegetative replication. We show here that the two parts of the protein are independently transported by the type IV pathway. Part of the domain containing the catalytic activity, as well as an adjacent region, is required in each case, but the required regions do not physically overlap. Both transport systems contribute to the overall frequency of conjugative transfer. MobB is a small protein, encoded within mobA but in a different reading frame, that stabilizes the relaxase at oriT. MobB is required for efficient type IV transport of both the complete relaxase and its two, separate functional halves. MobB inserts into the membrane and could thus stabilize the association between the relaxase and the type IV transfer apparatus.
质粒R1162的松弛酶是一种大型蛋白质，对接合转移至关重要，且具有两种不同的、物理上分离的催化活性。N端一半在转移起始点（oriT）切割其中一条DNA链，并与5'末端磷酸共价连接；C端一半是质粒营养复制起始所必需的引发酶。我们在此表明，该蛋白质的两个部分通过IV型途径独立运输。每种情况下都需要包含催化活性的部分结构域以及相邻区域，但所需区域在物理上并不重叠。两个运输系统都有助于接合转移的总体频率。MobB是一种小蛋白质，编码在mobA内但阅读框不同，它能在oriT处稳定松弛酶。MobB对于完整松弛酶及其两个独立功能部分的高效IV型运输都是必需的。MobB插入膜中，因此可以稳定松弛酶与IV型转移装置之间的结合。
