RNA interference is an evolutionarily conserved gene silencing pathway in which the endonuclease, Dicer cleaves double stranded RNA into small interfering RNAs. Dicer is a multidomain protein related to the RNase III protein family. Dicer is required by the RNA interference and small temporal RNA (stRNA) pathways to produce the active small interfering RNA (siRNA) component that represses gene expression. Dicer related RNA interference machinery is also involved in the formation of the heterochromatin structure in organisms such as yeast and higher vertebrate cells. In mammalian cells, both microRNAs (miRNAs) and small interfering RNAs (siRNAs) are thought to be loaded into the same RNA induced silencing complex (RISC), where they guide mRNA degradation or translation silencing depending on the complementarity of the target. Two transcript variants encoding the same protein have been identified.