Site-directed mutagenesis SDM disrupting the hairpin structure was performed using the QuickChange Mutagenesis Kit (Stratagene), according to the manufacturer's instructions. pGEM-3Z/H, containing 208 bp of the Pol b 3 0 UTR in the sense orientation, was used as a template for mutagenesis, resulting in the generation of pGEM-3Z/Hmut. Primers used for mutagenesis (changed nucleotides in bold):