Whitehead Institute for Biomedical Research, 9 Cambridge Center, Cambridge, MA 02142, USA.
Cell. 2011 Jul 22;146(2):262-76. doi: 10.1016/j.cell.2011.06.021.
The Dicer ribonuclease III (RNase III) enzymes process long double-stranded RNA (dsRNA) into small interfering RNAs (siRNAs) that direct RNA interference. Here, we describe the structure and activity of a catalytically active fragment of Kluyveromyces polysporus Dcr1, which represents the noncanonical Dicers found in budding yeasts. The crystal structure revealed a homodimer resembling that of bacterial RNase III but extended by a unique N-terminal domain, and it identified additional catalytic residues conserved throughout eukaryotic RNase III enzymes. Biochemical analyses showed that Dcr1 dimers bind cooperatively along the dsRNA substrate such that the distance between consecutive active sites determines the length of the siRNA products. Thus, unlike canonical Dicers, which successively remove siRNA duplexes from the dsRNA termini, budding-yeast Dicers initiate processing in the interior and work outward. The distinct mechanism of budding-yeast Dicers establishes a paradigm for natural molecular rulers and imparts substrate preferences with ramifications for biological function.
Dicer 核糖核酸酶 III（RNase III）酶将长双链 RNA（dsRNA）加工成小干扰 RNA（siRNA），从而指导 RNA 干扰。在这里，我们描述了 Kluyveromyces polysporus Dcr1 的具有催化活性的片段的结构和活性，它代表了在出芽酵母中发现的非典型 Dicer。晶体结构显示了一个类似于细菌 RNase III 的同源二聚体，但通过一个独特的 N 端结构域延伸，并且确定了整个真核 RNase III 酶保守的其他催化残基。生化分析表明，Dcr1 二聚体沿着 dsRNA 底物协同结合，使得相邻活性位点之间的距离决定 siRNA 产物的长度。因此，与经典的 Dicer 不同，经典的 Dicer 从 dsRNA 末端依次去除 siRNA 双链，出芽酵母的 Dicer 从内部开始加工并向外工作。出芽酵母 Dicer 的独特机制为天然分子标尺建立了一个范例，并赋予了具有生物学功能的底物偏好。
