post transcriptional interference rna interference PSI-MI RNA interference (RNAi) is a post-transcriptional gene silencing method reproducing a naturally occurring phenomena. RNAi is the process whereby double-stranded RNA (dsRNA) induces the sequence-specific degradation of homologous mRNA. RNAi or dsRNA-induced silencing phenomena are present in evolutionarily diverse organisms, e.g., nematodes, plants, fungi, and trypanosomes. The mechanisms by which RNAi works is initiated by a progressive cleavage of dsRNA into 21 to 23 nucleotide (nt) short interfering RNAs (siRNAs). These native siRNA duplexes are then incorporated into a protein complex called RNA-induced silencing complex (RISC). ATP-dependent unwinding of the siRNA duplex generates an active RISC complex. Guided by the antisense strand of siRNA, the active RISC complex recognizes and cleaves the corresponding mRNA. rnai MI:0256