Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, Saint Louis, Missouri, USA.
Nat Struct Mol Biol. 2010 Oct;17(10):1210-7. doi: 10.1038/nsmb.1901. Epub 2010 Sep 19.
E. coli RecBCD is a DNA helicase with two ATPase motors (RecB, a 3'→5' translocase, and RecD, a 5'→3' translocase) that function in repair of double-stranded DNA breaks. The RecBC heterodimer, with only the RecB motor, remains a processive helicase. Here we examined RecBC translocation along single-stranded DNA (ssDNA). Notably, we found RecBC to have two translocase activities: the primary translocase moves 3'→5', whereas the secondary translocase moves RecBC along the opposite strand of a forked DNA at a similar rate. The secondary translocase is insensitive to the ssDNA backbone polarity, and we propose that it may fuel RecBCD translocation along double-stranded DNA ahead of the unwinding fork and ensure that the unwound single strands move through RecBCD at the same rate after interaction with a crossover hot-spot indicator (Chi) sequence.
大肠杆菌 RecBCD 是一种具有两个 ATP 酶马达（RecB，3'→5' 转位酶，和 RecD，5'→3' 转位酶）的 DNA 解旋酶，其在双链 DNA 断裂的修复中起作用。仅有 RecB 马达的 RecBC 异二聚体仍然是一个连续的解旋酶。在这里，我们研究了 RecBC 在单链 DNA（ssDNA）上的易位。值得注意的是，我们发现 RecBC 具有两种转位酶活性：主要转位酶移动 3'→5'，而次要转位酶以相似的速度沿分叉 DNA的相反链移动 RecBC。次要转位酶对 ssDNA 骨架极性不敏感，我们提出它可能在解旋叉之前为 RecBCD 沿着双链 DNA 的易位提供动力，并确保与交叉热点指示剂（Chi）序列相互作用后解开的单链以相同的速度通过 RecBCD 移动。
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