In the first processing step, which occurs in the nucleus, the pri-miRNA is cleaved into pre-miRNA (an approximately 70-nucleotide hairpin stem loop intermediate) by a microprocessor complex that consists of Drosha, an RNase III enzyme, and DGCR8, a double-stranded RNA-binding domain (dsRBD) protein [7].
Some well-characterised RNA-binding domains (RBD, also known as RNP domain and RNA recognition motif, RRM) include the following: K-homology (KH) domain (type I and type II), RGG (Arg-Gly-Gly) box, Sm domain, DEAD/DEAH box, zinc finger (ZnF), double-stranded RNA-binding domain (dsRBD), cold-shock domain, Pumilio/FBF (PUF or Pum-HD) domain and the Piwi/Argonaute/Zwille (PAZ) domain [24].