• Open Access

The molecular machines that mediate microRNA maturation


Correspondence to: Ian J. MACRAE,
Department of Molecular Biology,
The Scripps Research Institute, La Jolla, CA 92037, USA.
Tel.: +(858) 784-2932
Fax: +(858) 784-7579
E-mail: macrae@scripps.edu


  • • Introduction
  • • miRNAs originate from primary RNA transcripts
  • • The Microprocessor initiates miRNA processing
  • • Nuclear proteins regulate activity of the Microprocessor
  • • Intronic pre-miRNAs can bypass the Microprocessor
  • • The Exportin-5 Complex transports pre-miRNA to the cytoplasm
  • • The RISC-Loading Complex completes miRNA maturation
  • • Mature miRNAs silence target genes from within RISC
  • • Discussion and future directions


MicroRNAs (miRNA) are small RNAs that regulate the translation of thousands of message RNAs and play a profound role in mammalian biology. Over the past 5 years, significant advances have been made towards understanding the pathways that generate miRNAs and the mechanisms by which miRNAs exert their regulatory functions. An emerging theme is that miRNAs are both generated by and utilized by large and complex macromolecular assemblies. Here, we review the biology of mammalian miRNAs with a focus on the macromolecular complexes that generate and control the biogenesis of miRNAs.