Kruklitis R, Welty D J, Nakai H
Department of Biochemistry and Molecular Biology, Georgetown University Medical Center, Washington, DC 20007, USA.
EMBO J. 1996 Feb 15;15(4):935-44.
During transposition bacteriophage Mu transposase (MuA) catalyzes the transfer of a DNA strand at each Mu end to target DNA and then remains tightly bound to the Mu ends. Initiation of Mu DNA replication on the resulting strand transfer complex (STC1) requires specific host replication proteins and host factors from two partially purified enzyme fractions designated Mu replication factors alpha and beta (MRFalpha and beta). Escherichia coli ClpX protein, a molecular chaperone, is a component required for MRFalpha activity, which removes MuA from DNA for the establishment of a Mu replication fork. ClpX protein alters the conformation of DNA-bound MuA and converts STC1 to a less stable form (STC2). One or more additional components of MRFalpha (MRFalpha2) displace MuA from STC2 to form a nucleoprotein complex (STC3), that requires the specific replication proteins and MRFbeta for Mu DNA synthesis. MuA present in STC2 is essential for its conversion to STC3. If MuA is removed from STC2, Mu DNA synthesis no longer requires MRFalpha2, MRFbeta and the specific replication proteins. These results indicate that ClpX protein activates MuA in STC1 so that it can recruit crucial host factors needed to initiate Mu DNA synthesis by specific replication enzymes.
在转座过程中，噬菌体Mu转座酶（MuA）催化每条Mu末端的一条DNA链转移到靶DNA上，然后紧密结合在Mu末端。在产生的链转移复合物（STC1）上启动Mu DNA复制需要特定的宿主复制蛋白以及来自两个部分纯化的酶组分（称为Mu复制因子α和β，即MRFα和MRFβ）的宿主因子。大肠杆菌ClpX蛋白作为一种分子伴侣，是MRFα活性所需的一个组分，它将MuA从DNA上移除，以建立Mu复制叉。ClpX蛋白改变与DNA结合的MuA的构象，并将STC1转变为一种较不稳定的形式（STC2）。MRFα的一个或多个其他组分（MRFα2）将MuA从STC2上置换下来，形成一种核蛋白复合物（STC3），该复合物进行Mu DNA合成需要特定的复制蛋白和MRFβ。STC2中存在的MuA对于其转变为STC3至关重要。如果将MuA从STC2中移除，Mu DNA合成不再需要MRFα2、MRFβ和特定的复制蛋白。这些结果表明，ClpX蛋白激活STC1中的MuA，使其能够募集特定复制酶启动Mu DNA合成所需的关键宿主因子。
