Oligonucleotides and preparation of RNAs

The ssRNA and single-stranded DNA (ssDNA) substrates were chemically synthesized (ST pharm Co. Ltd. Seoul, Korea). The 5'-ppp ssRNAs were synthesized by in vitro transcription using T7 polymerase, as described previously (18). For generating duplexes, RNA or DNA oligonucleotides were mixed in annealing buffer (10 mM Tris-HCl, pH 7.5, 100 mM NaCl, and 1 mM EDTA), boiled at 85℃ for 3 min, and incubated at 25℃ for 20 min. Where indicated, oligonucleotides were 5'-phosphorylated using T4 polynucleotide kinase (TaKaRa, Tokyo, Japan). Yeast tRNA and polyinosinic:polycytidylic acid (poly I:C) nucleotides were purchased from Sigma (St. Louis, MO, USA).