Brown J Lesley, He Jiuya, Sherratt David J, Stark W Marshall, Boocock Martin R
Institute of Biomedical and Life Sciences, University of Glasgow, 56 Dumbarton Road, Glasgow G11 6NU, Scotland, UK.
J Mol Biol. 2002 May 31;319(2):371-83. doi: 10.1016/S0022-2836(02)00309-1.
"Looping" interactions of distant sites on DNA molecules, mediated by DNA-binding proteins, feature in many regulated genetic processes. We used plasmids containing up to six res recombination sites for Tn3 resolvase to analyse looping interactions (synapsis) in this system. We observed that in plasmids with four or more res sites, certain pairs of sites recombine faster than others. The relative rates of recombination depend on the number, relative orientation, and arrangement of the sites. To account for the differences in rate, we propose that pairing interactions between resolvase-bound res sites are in a state of rapid flux, leading to configurations in which the maximum number of sites within each supercoiled substrate molecule are synapsed in a topologically simple arrangement. Recombination rates reflect the steady state concentrations of these synapse configurations. Our results are at variance with models for selective synapsis that rely on ordered motions within supercoiled DNA, "slithering" or "tracking", but are compatible with models that call for reversible synapsis of pairs of sites by random collision, followed by formation of an interwound productive synapse.
由DNA结合蛋白介导的DNA分子上远距离位点的“环化”相互作用，在许多受调控的遗传过程中都有体现。我们使用了含有多达六个Tn3解离酶的res重组位点的质粒，来分析该系统中的环化相互作用（联会）。我们观察到，在含有四个或更多res位点的质粒中，某些位点对的重组速度比其他位点对更快。重组的相对速率取决于位点的数量、相对方向和排列方式。为了解释速率差异，我们提出，解离酶结合的res位点之间的配对相互作用处于快速变化的状态，导致形成这样的构型：每个超螺旋底物分子内的最大数量的位点以拓扑学上简单的排列方式发生联会。重组速率反映了这些联会构型的稳态浓度。我们的结果与依赖于超螺旋DNA内有序运动（“滑动”或“追踪”）的选择性联会模型不同，但与通过随机碰撞使位点对进行可逆联会，随后形成缠绕的有效联会的模型相符。
