Biek D P, Cohen S N
Department of Microbiology and Immunology, University of Kentucky Medical Center, Lexington 40536.
J Bacteriol. 1992 Feb;174(3):785-92. doi: 10.1128/jb.174.3.785-792.1992.
Integration host factor (IHF), a multifunctional protein of E. coli, normally is required for the replication of plasmid pSC101. T. T. Stenzel, P. Patel, and D. Bastia (Cell 49:709-717, 1987) have reported that IHF binds to a DNA locus near the pSC101 replication origin and enhances a static bend present in this region; mutation of the IHF binding site affects the plasmid's ability to replicate. We report here studies indicating that the requirement for IHF binding near the pSC101 replication origin is circumvented partially or completely by (i) mutation of the plasmid-encoded repA (replicase) gene or the chromosomally encoded topA gene, (ii) the presence on the plasmid of the pSC101 partition (par) locus, or (iii) replacement of the par locus by a strong transcriptional promoter. With the exception of the repA mutation, the factors that substitute for a functional origin region IHF binding site are known to alter plasmid topology by increasing negative DNA supercoiling, as does IHF itself. These results are consistent with the proposal that IHF binding near the pSC101 replication origin promotes plasmid replication by inducing a conformational change leading to formation of a repA-dependent DNA-protein complex. A variety of IHF-independent mechanisms can facilitate formation of the putative replication-initiation complex.
整合宿主因子（IHF）是大肠杆菌的一种多功能蛋白质，通常是质粒pSC101复制所必需的。T. T. 施滕泽尔、P. 帕特尔和D. 巴斯蒂亚（《细胞》49:709 - 717，1987年）报告称，IHF与pSC101复制起点附近的一个DNA位点结合，并增强该区域存在的一个静态弯曲；IHF结合位点的突变会影响质粒的复制能力。我们在此报告的研究表明，通过以下方式可部分或完全规避在pSC101复制起点附近对IHF结合的需求：（i）质粒编码的repA（复制酶）基因或染色体编码的topA基因发生突变，（ii）质粒上存在pSC101分配（par）位点，或（iii）用一个强转录启动子替代par位点。除了repA突变外，已知替代功能性起点区域IHF结合位点的因素会像IHF自身一样，通过增加负超螺旋来改变质粒拓扑结构。这些结果与以下提议一致，即在pSC101复制起点附近的IHF结合通过诱导构象变化促进质粒复制，导致形成依赖repA的DNA - 蛋白质复合物。多种不依赖IHF的机制可促进假定的复制起始复合物的形成。
