Komori H, Matsunaga F, Higuchi Y, Ishiai M, Wada C, Miki K
Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, USA.
EMBO J. 1999 Sep 1;18(17):4597-607. doi: 10.1093/emboj/18.17.4597.
The initiator protein (RepE) of F factor, a plasmid involved in sexual conjugation in Escherichia coli, has dual functions during the initiation of DNA replication which are determined by whether it exists as a dimer or as a monomer. A RepE monomer functions as a replication initiator, but a RepE dimer functions as an autogenous repressor. We have solved the crystal structure of the RepE monomer bound to an iteron DNA sequence of the replication origin of plasmid F. The RepE monomer consists of topologically similar N- and C-terminal domains related to each other by internal pseudo 2-fold symmetry, despite the lack of amino acid similarities between the domains. Both domains bind to the two major grooves of the iteron (19 bp) with different binding affinities. The C-terminal domain plays the leading role in this binding, while the N-terminal domain has an additional role in RepE dimerization. The structure also suggests that superhelical DNA induced at the origin of plasmid F by four RepEs and one HU dimer has an essential role in the initiation of DNA replication.
F 因子的引发蛋白（RepE）是一种参与大肠杆菌有性接合的质粒，在 DNA 复制起始过程中具有双重功能，这取决于它是以二聚体还是单体形式存在。RepE 单体作为复制引发剂起作用，但 RepE 二聚体作为自身阻遏物起作用。我们已经解析了与质粒 F 复制起点的迭代子 DNA 序列结合的 RepE 单体的晶体结构。RepE 单体由拓扑结构相似的 N 端和 C 端结构域组成，尽管这两个结构域之间缺乏氨基酸相似性，但通过内部伪二重对称相互关联。两个结构域以不同的结合亲和力与迭代子（19 碱基对）的两个大沟结合。C 端结构域在这种结合中起主导作用，而 N 端结构域在 RepE 二聚化中具有额外作用。该结构还表明，由四个 RepE 和一个 HU 二聚体在质粒 F 起点诱导的超螺旋 DNA 在 DNA 复制起始中具有重要作用。
