Interfering RNA (RNAi) - stage 4. The RISC complex (RNA-induced silencing complex) fixes to the whole composed of the Dicer protein and the fragment of double-stranded RNA. One of the arms of the RNA is released (passenger RNA) whereas the other remains linked to the RISC (RNA guide). A free Dicer protein is visible on the side. Interfering RNA is a mean for the cell to destroy the RNA parasites (viruses RNA, transposons). The Dicer protein, a type III ribonuclease, fixes to the double-stranded RNA, and cleaves it into fragments of 21-25 nucleotides. Then, a proteic complex (named RISC for RNA-induced silencing complex) fixes to the whole Dicer-fragment of double-stranded RNA. One of the RNA strands is then eliminated (passenger RNA), whereas the other (RNA guide) remains linked to the RISC-Dicer complex. By sequence complementarity, the RNA guide then fixes to the specific RNA molecule of the virus or transposon. The latter is then cut by the endonuclease activity of RISC (cleavage) then destroyed. The cell then eliminates all foreign RNA. RNA interference is currently under study to turn off individual gene expression (silencing) in the framework of the development of new therapies. See. images 1072907, 1073007, 1073107, 1073207, 1073307 and 1073407 for the detailed explanation of the RNA interference.