 RNAi is an RNA @-@ dependent gene silencing process that is controlled by the RNA @-@ induced silencing complex ( RISC ) and is initiated by short double @-@ stranded RNA molecules in a cell 's cytoplasm , where they interact with the catalytic RISC component argonaute . When the dsRNA is exogenous ( coming from infection by a virus with an RNA genome or laboratory manipulations ) , the RNA is imported directly into the cytoplasm and cleaved to short fragments by Dicer . The initiating dsRNA can also be endogenous ( originating in the cell ) , as in pre @-@ microRNAs expressed from RNA @-@ coding genes in the genome . The primary transcripts from such genes are first processed to form the characteristic stem @-@ loop structure of pre @-@ miRNA in the nucleus , then exported to the cytoplasm . Thus , the two dsRNA pathways , exogenous and endogenous , converge at the RISC . 
