UNWINDING AND REWINDING OF DNA BY THE RECBC ENZYME
UNWINDING AND REWINDING OF DNA BY THE RECBC ENZYME
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DOI：
10.1016/0092-8674(80)90355-4
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发表时间：
1980-01-01
期刊：
影响因子：
64.5
通讯作者：
SMITH, GR
中科院分区：
文献类型：
--
作者：
TAYLOR, A;SMITH, GR
在生理条件下，[大肠杆菌] RecBc酶（核酸外切酶V）对双链DNA的初始作用是DNA链的解旋。通过EM，检查了该解旋反应的初始产物。当这种反应在DNA结合蛋白存在下进行时，在双链体DNA的末端和远离DNA分子末端的位置都可以看到解旋结构。末端和内部解旋结构都以约300个核苷酸/秒的速度沿DNA沿着进行，并且两种类型结构中的单链环以约100个核苷酸/秒的速度扩大。在内部解旋中，DNA必须以大约200个核苷酸/秒的速度在酶后面重绕。这种结构不会出现在超螺旋或切口的环状DNA上，这表明它们的形成需要自由末端。在没有DNA结合蛋白的情况下，只看到内部解旋结构，这表明内部结构是由末端解旋通过其解旋的单链尾部的碱基配对形成的。一个模型，其中包括这些结构，它是与以前的观察解旋和降解作用的酶是一致的。在这个模型中，酶通过在自身前面解开DNA并在自身后面倒回DNA来穿过双链体DNA。由RecBC酶产生的内部解绕可能在遗传重组的初始突触步骤中是活跃的。
Under physiological conditions the initial action of the [Escherichia coli] RecBc enzyme (exonuclease V) on duplex DNA is unwinding of the DNA strands. By EM, the initial products of this unwinding reaction was examined. When such reactions are carried out in the presence of DNA binding protein, unwinding structures are seen both at the terminus of the duplex DNA and at locations remote from the ends of the DNA molecule. Both terminal and internal unwinding structures proceed along DNA at about 300 nucleotides/second, and the single-stranded loops in both types of structure enlarge at about 100 nucleotides/second. In the internal unwindings DNA must be rewound behind the enzyme at about 200 nucleotides/second. The structures do not occur on supercoiled or nicked circular DNA, indicating that free ends are needed for their formation. In the absence of DNA binding protein only internal unwinding structures are seen, suggesting that the internal structures are formed from the terminal unwindings by base-pairing of their unwound single-strand tails. A model which incorporates these structures is presented, and it is consistent with previous observations on the unwinding and degradative actions of the enzyme. In this model the enzyme travels through duplex DNA by unwinding the DNA ahead of itself and rewinding it behind itself. The internal unwindings produced by the RecBC enzyme could be active in the initial synapsis step in genetic recombination.