Taylor A F, Smith G R
J Mol Biol. 1985 Sep 20;185(2):431-43. doi: 10.1016/0022-2836(85)90414-0.
The RecBC enzyme of Escherichia coli promotes genetic recombination of phage or bacterial chromosomes. The purified enzyme travels through duplex DNA, unwinding and rewinding the DNA with the transient production of potentially recombinogenic single-stranded DNA. The studies reported here are aimed at understanding which chromosomal forms allow the entry of RecBC enzyme and hence may undergo RecBC enzyme-mediated recombination. Circular duplex molecules, whether covalently closed, nicked or containing single-stranded gaps of 10 to 774 nucleotides, are not detectably unwound by RecBC enzyme. Linear duplex molecules are readily unwound if they have a nearly flush-ended terminus whose 5' and 3' ends are offset by no more than about 25 nucleotides; molecules with longer single-stranded tails are poorly bound by RecBC enzyme and are infrequently unwound. The single-strand endonuclease activity of RecBC enzyme can slowly cleave gapped circles to produce molecules presumably capable of being unwound. These results provide an enzymatic basis for the recombinogenicity of double-stranded DNA ends established from genetic studies of RecBC enzyme and Chi sites, recognition sites for RecBC enzyme-mediated DNA strand cleavage.
大肠杆菌的RecBC酶促进噬菌体或细菌染色体的基因重组。纯化后的该酶穿梭于双链DNA中，通过短暂产生潜在的可重组单链DNA来解旋和重新缠绕DNA。本文报道的研究旨在了解哪些染色体形式允许RecBC酶进入，因此可能会发生RecBC酶介导的重组。环状双链分子，无论是共价闭合、有切口还是含有10至774个核苷酸的单链缺口，都不会被RecBC酶明显解旋。如果线性双链分子的末端几乎平齐，其5'和3'末端的偏移不超过约25个核苷酸，则很容易被解旋；具有较长单链尾巴的分子与RecBC酶的结合较差，很少被解旋。RecBC酶的单链内切核酸酶活性可以缓慢切割有缺口的环状分子，以产生可能能够被解旋的分子。这些结果为从RecBC酶和Chi位点（RecBC酶介导的DNA链切割的识别位点）的遗传研究中确定的双链DNA末端的重组性提供了酶学基础。
