Adzuma K
The Rockefeller University, New York, New York 10021, USA.
J Biol Chem. 1998 Nov 20;273(47):31565-73. doi: 10.1074/jbc.273.47.31565.
The RecA protein of Escherichia coli is a prototype of the RecA/Rad51 family of proteins that exist in virtually all the organisms. In a process called DNA synapsis, RecA first polymerizes onto a single-stranded DNA (ssDNA) molecule; the resulting RecA-ssDNA complex then searches for and binds to a double-stranded DNA (dsDNA) molecule containing the almost identical, or "homologous, " sequence. The RecA-ssDNA complex thus can be envisioned as a sequence-specific binding entity. How does the complex search for its target buried within nonspecific sequences? One possible mechanism is the sliding mechanism, in which the complex first binds to a dsDNA molecule nonspecifically and then linearly diffuses, or slides, along the dsDNA. To understand the mechanism of homology search by RecA, this sliding model was tested. A plasmid containing four homologous targets in tandem was constructed and used as the dsDNA substrate in the synapsis reaction. If the sliding is the predominant search mode, the two outermost targets should act as more efficient targets than the inner targets. No such positional preference was observed, indicating that a long range sliding of the RecA-ssDNA complex does not occur. These and other available data can be adequately explained by a simple three-dimensional random collision mechanism.
大肠杆菌的RecA蛋白是几乎存在于所有生物体中的RecA/Rad51蛋白家族的原型。在一个称为DNA联会的过程中，RecA首先在单链DNA（ssDNA）分子上聚合；然后，产生的RecA-ssDNA复合物寻找并结合到一个含有几乎相同或“同源”序列的双链DNA（dsDNA）分子上。因此，RecA-ssDNA复合物可以被设想为一个序列特异性结合实体。该复合物如何在非特异性序列中寻找其目标呢？一种可能的机制是滑动机制，即复合物首先非特异性地结合到一个dsDNA分子上，然后沿着dsDNA线性扩散或滑动。为了理解RecA进行同源性搜索的机制，对这种滑动模型进行了测试。构建了一个串联含有四个同源靶点的质粒，并将其用作联会反应中的dsDNA底物。如果滑动是主要的搜索模式，那么最外侧的两个靶点应该比内侧的靶点更有效地发挥作用。但未观察到这种位置偏好，这表明RecA-ssDNA复合物不会发生长距离滑动。这些以及其他现有数据可以通过一个简单的三维随机碰撞机制得到充分解释。
