Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, Connecticut 06520, USA.
J Biol Chem. 2010 Apr 9;285(15):11692-703. doi: 10.1074/jbc.M109.088559. Epub 2010 Jan 28.
The superfamily 2 vaccinia viral helicase nucleoside triphosphate phosphohydrolase-II (NPH-II) exhibits robust RNA helicase activity but typically displays little activity on DNA substrates. NPH-II is thus believed to make primary contacts with backbone residues of an RNA substrate. We report an unusual nucleobase bias, previously unreported in any superfamily 1 or 2 helicase, whereby purines are heavily preferred as components of both RNA and DNA tracking strands. The observed sequence bias allows NPH-II to efficiently unwind a DNA x RNA hybrid containing a purine-rich DNA track derived from the 3'-untranslated region of an early vaccinia gene. These results provide insight into potential biological functions of NPH-II and the role of sequence in targeting NPH-II to appropriate substrates. Furthermore, they demonstrate that in addition to backbone contacts, nucleotide bases play an important role in modulating the behavior of NPH-II. They also establish that processive helicase enzymes can display sequence selectivity.
超家族 2 痘病毒解旋酶核苷三磷酸磷酸水解酶-II（NPH-II）表现出强大的 RNA 解旋酶活性，但通常对 DNA 底物的活性较小。因此，人们认为 NPH-II 与 RNA 底物的骨架残基首先发生接触。我们报告了一种不寻常的核碱基偏好，以前在任何超家族 1 或 2 解旋酶中都没有报道过，即嘌呤作为 RNA 和 DNA 跟踪链的组成部分被强烈偏爱。观察到的序列偏好使 NPH-II 能够有效地解开含有富含嘌呤的 DNA 轨道的 DNA x RNA 杂交体，该 DNA 轨道来自早期痘病毒基因的 3'-非翻译区。这些结果深入了解了 NPH-II 的潜在生物学功能以及序列在将 NPH-II 靶向适当底物中的作用。此外，它们表明除了骨架接触外，核苷酸碱基在调节 NPH-II 行为方面也起着重要作用。它们还证实，除了连续的解旋酶酶外，还可以显示序列选择性。
