RNA interference protein, molecular model. Known as dicer, this RNA interference protein (coloured strands) is bound to and cutting up a strand of ribonucleic acid (RNA, white solid areas). Dicer is an RNAase enzyme that cleaves double-stranded RNA into short fragments called small interfering RNA (siRNA). The different domains of dicer are coloured here (from left): PAZ domain (purple), Plattform (red), RNAse IIIa (yellow), RNAse IIIb (light blue), and a bridging domain (dark blue).