Department of Biochemistry, University of Utah, Salt Lake City, UT 84112, USA.
Mol Cell. 2011 Mar 4;41(5):589-99. doi: 10.1016/j.molcel.2011.02.005.
The role of Dicer's helicase domain is enigmatic, but in vivo it is required for processing certain endogenous siRNA, but not miRNA. By using Caenorhabditis elegans extracts or purified Drosophila Dicer-2 we compared activities of wild-type enzymes and those containing mutations in the helicase domain. We found the helicase domain was essential for cleaving dsRNA with blunt or 5'-overhanging termini, but not those with 3' overhangs, as found on miRNA precursors. Further, blunt termini, but not 3' overhangs, led to increased siRNAs from internal regions of dsRNA; this activity required ATP and a functional helicase domain. Our data suggest that blunt or 5'-overhanging termini engage Dicer's helicase domain to facilitate accumulation of siRNAs from internal regions of a dsRNA, an activity suited for processing long siRNA precursors of low abundance, but not necessary for the single cleavage required for miRNA processing.
Dicer 的解旋酶结构域的作用尚不清楚，但在体内，它需要处理某些内源性 siRNA，但不需要 miRNA。我们使用秀丽隐杆线虫提取物或纯化的果蝇 Dicer-2 比较了野生型酶和含有解旋酶结构域突变的酶的活性。我们发现解旋酶结构域对于切割具有平头或 5'突出末端的 dsRNA 是必需的，但对于具有 3'突出末端的 dsRNA 则不是，而 miRNA 前体就具有 3'突出末端。此外，平头末端而不是 3'突出末端会导致 dsRNA 内部区域产生更多的 siRNA；这种活性需要 ATP 和功能齐全的解旋酶结构域。我们的数据表明，平头或 5'突出末端与 Dicer 的解旋酶结构域结合，有助于从 dsRNA 的内部区域积累 siRNA，这种活性适合处理低丰度的长 siRNA 前体，但对于 miRNA 加工所需的单个切割并非必需。
