dsRNAs homologous to firefly luciferase provoked a sequence specific effect, producing a degree of suppression that was slightly more potent than was observed upon transfection with cognate 21-ntsiRNA(ref.5;Fig.4A).However,with long dsRNA triggers, the specific effect was superimposed upon a generalized suppression of reporter gene expression that was presumably because of PKR activation (Fig. 4B).