A sequence of single-stranded RNA, that is 20-25 nucleotides in length, which is transcribed from DNA but is not translated into a protein. This nucleic acid may regulate the transcription or translation of other genes.

A type of RNA found in cells and in blood. MicroRNAs are smaller than many other types of RNA and can bind to messenger RNAs (mRNAs) to block them from making proteins. MicroRNAs are being studied in the diagnosis and treatment of cancer.

Small regulatory antisense RNA that represses the genetic translation of homologous target RNA; process by which they are generated is related to the process that produces small interfering RNA.

Small double-stranded, non-protein coding RNAs, 21-25 nucleotides in length generated from single-stranded microRNA gene transcripts by the same RIBONUCLEASE III, Dicer, that produces small interfering RNAs (RNA, SMALL INTERFERING). They become part of the RNA-INDUCED SILENCING COMPLEX and repress the translation (TRANSLATION, GENETIC) of target RNA by binding to homologous 3'UTR region as an imperfect match. The small temporal RNAs (stRNAs), let-7 and lin-4, from C. elegans, are the first 2 miRNAs discovered, and are from a class of miRNAs involved in developmental timing.