Dicer

Dicer is an RNase III-like enzyme. It contains two RNase III domains and one PAZ domain. The distance between these two domains is determined by a helical region, the length of which determines the length of the siRNAs produced. Dicer catalyzes the first step of RNA interference and initiates the formation of the RNA-induced silencing complex (RISC ), whose endonuclease "argonaute" is able to degrade mRNA whose sequence is complementary to the resulting siRNA.

Using knockout mosses (a knockout moss is a moss plant in which one or more genes are specifically switched off by means of a targeted genetic modification, so-called gene targeting/gene knockout), it was shown that DCL1b, one of four Dicer proteins of Physcomitrella, is not required for miRNA biogenesis, but for cutting the target transcripts. This led to the elucidation of a new mechanism of gene regulation.