miRNAs/Small Noncoding RNAs

microRNAs (miRNAs) are approximately 22 nucleotide long, small noncoding RNAs that function in posttranscriptional gene silencing and play fundamental roles in biology. miRNAs are produced by sequential cleavage of precursor RNA transcripts by the Ribonuclease III enzymes, Drosha and Dicer. Then miRNAs are loaded to the effector protein, Argonaute, forming miRNA-induced silencing complex (miRISC). miRISC binds mRNA targets via sequence complementarity and silences the targets by translational repression and/or mRNA destabilization. Human genome contains over 1800 miRNAs, which target 60% of human mRNAs. Mutations in the miRNA genes and the miRNA pathway genes are associated with various human diseases including cancers.