Positive torsional strain causes the formation of a four-way junction at replication forks
Positive torsional strain causes the formation of a four-way junction at replication forks
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DOI：
10.1074/jbc.m006736200
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发表时间：
2001-01-26
影响因子：
4.8
通讯作者：
Cozzarelli, NR
中科院分区：
文献类型：
--
作者：
Postow, L;Ullsperger, C;Cozzarelli, NR
DNA复制叉的前进需要亲本双螺旋的解旋。这反过来又产生了一个正的超螺旋应力，（+）-Δ Lk，它必须通过拓扑异构酶松弛才能进行复制。令人惊讶的是，具有（+）-Δ Lk的部分复制的质粒不是超螺旋的，复制的臂在前环烷烃中也不是相互缠绕的。这些分子的电泳迁移率表明它们没有净蠕动。相反，（+）-Delta Lk被复制叉的回归吸收。当亲本DNA链重新退火时，所产生的移位的子链彼此碱基配对以在复制叉处形成四向连接，其在重组中与霍利迪连接局部相同。我们通过限制性内切酶消化表明，连接可以在复制的末端或起点形成，并且我们用扫描力显微镜观察了结构。我们讨论了可能的生理意义的交界处停滞在体内复制。
The advance of a DNA replication fork requires an unwinding of the parental double helix. This in turn creates a positive superhelical stress, a (+)-Delta Lk, that must be relaxed by topoisomerases for replication to proceed. Surprisingly, partially replicated plasmids with a (+)-Delta Lk were not supercoiled nor were the replicated arms interwound in precatenanes. The electrophoretic mobility of these molecules indicated that they have no net writhe. Instead, the (+)-Delta Lk is absorbed by a regression of the replication fork. As the parental DNA strands re-anneal, the resultant displaced daughter strands base pair to each other to form a four-way junction at the replication fork, which is locally identical to a Holliday junction in recombination. We showed by restriction endonuclease digestion that the junction can form at either the terminus or the origin of replication and we visualized the structure with scanning force microscopy. We discuss possible physiological implications of the junction for stalled replication in vivo.