Matson S W
Department of Biology, University of North Carolina, Chapel Hill 27599.
Proc Natl Acad Sci U S A. 1989 Jun;86(12):4430-4. doi: 10.1073/pnas.86.12.4430.
DNA helicase II is a well-characterized Escherichia coli enzyme capable of unwinding duplex DNA and known to be involved in both methyl-directed mismatch repair and excision repair of pyrimidine dimers. Here it is shown that this enzyme also catalyzes the ATP-dependent unwinding of a DNA.RNA hybrid consisting of a radioactively labeled RNA molecule annealed on M13 single-stranded DNA. The DNA.RNA unwinding reaction required less protein to unwind more base pairs than the corresponding unwinding of duplex DNA. In addition, the rate of unwinding of the DNA.RNA hybrid was more than an order of magnitude faster than unwinding of a DNA partial duplex of similar length. The unwinding of the DNA.RNA hybrid is a property unique to helicase II since helicase I, Rep protein, and helicase IV failed to catalyze the reaction. In light of these results it seems likely that helicase II is involved in some previously unrecognized aspect of nucleic acid metabolism, in addition to its known roles in DNA repair reactions.
DNA解旋酶II是一种已被充分表征的大肠杆菌酶，能够解开双链DNA，并且已知参与甲基导向的错配修复和嘧啶二聚体的切除修复。本文表明，这种酶还能催化由放射性标记的RNA分子退火到M13单链DNA上形成的DNA·RNA杂交体的ATP依赖性解旋。与双链DNA的相应解旋相比，DNA·RNA解旋反应解开更多碱基对所需的蛋白质更少。此外，DNA·RNA杂交体的解旋速度比类似长度的DNA部分双链体的解旋速度快一个多数量级。DNA·RNA杂交体的解旋是解旋酶II独有的特性，因为解旋酶I、Rep蛋白和解旋酶IV都不能催化该反应。鉴于这些结果，除了其在DNA修复反应中的已知作用外，解旋酶II似乎还参与了核酸代谢中一些以前未被认识的方面。
