title: Dicer's helicase domain discriminates dsRNA termini to promote an altered reaction mode.
abstract: 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.
authors.affiliation: Department of Biochemistry, University of Utah, Salt Lake City, UT 84112, USA.
authors.forename: Noah C
authors.initials: NC
authors.lastname: Welker
authors.forename: Tuhin S
authors.initials: TS
authors.lastname: Maity
authors.forename: Xuecheng
authors.initials: X
authors.lastname: Ye
authors.forename: P Joseph
authors.initials: PJ
authors.lastname: Aruscavage
authors.forename: Ammie A
authors.initials: AA
authors.lastname: Krauchuk
authors.forename: Qinghua
authors.initials: Q
authors.lastname: Liu
authors.forename: Brenda L
authors.initials: BL
authors.lastname: Bass
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry; D020816:Amino Acid Motifs; D000818:Animals; D017173:Caenorhabditis elegans; D004330:Drosophila; D035683:MicroRNAs / Q000378:metabolism; D008954:Models, Biological; D009154:Mutation; D017434:Protein Structure, Tertiary; D012330:RNA, Double-Stranded / Q000737:chemistry / Q000235:genetics*; D034741:RNA, Small Interfering / Q000378:metabolism; D043244:Ribonuclease III / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D035683:MicroRNAs; D012330:RNA, Double-Stranded; D034741:RNA, Small Interfering; D000255:Adenosine Triphosphate; D043244:Ribonuclease III