Argonaute protein and RNA. Molecular model of the argonaute protein (green) with a guide segment of ribonucleic acid (RNA, orange). This protein forms the RNA-induced silencing complex (RISC) along with a small interfering RNA (ribonucleic acid) molecule. RISC plays a role in gene regulation and defence against viral infection. This example is from the yeast Vanderwaltozyma polyspora.