(miRNA) a small noncoding ribonucleotide-based (RNA) regulators of gene expression. These recently discovered small RNA molecules (18-24 nucleotides) negatively regulate target mRNAs and appear to have a role in many developmental processes as well as in the adult. (See also "Dicer") There is also another class of small RNAs involved in gene expression present in cells, small interfering RNAs (siRNAs), generated from double-stranded RNA (dsRNA) precursors.

Micro-RNAs (miRNA) are single-stranded RNAs of 22-nt that are processed from ~70-nt hairpin RNA precursors by Rnase III nuclease Dicer. Similar to siRNAs, miRNAs can silence gene activity via destruction of homologous mRNA in plants or blocking its translation in plants and animals.

A group of small RNA molecules, distinct from but related to small interference RNA (siRNA), that can prevent the expression of certain genes.