miRNA

abbr. for microRNA; other name: tiny RNA; any of various RNA species that are 21 — 25 nt long and may be single- or double-stranded. They have been found in animals, including Drosophila and Caenorhabditis elegans, and in plants. The term encompasses small interfering RNA (siRNA) and small temporal RNA (stRNA), as well as miRNA proper. miRNAs are transcribed as parts of longer RNA molecules and processed in the nucleus by the dsRNA ribonuclease Drosha to hairpin structures 70 — 100 nucleotides long. These are transported to the cytoplasm where they are digested to 21 — 23-mers by the dsRNA ribonuclease Dicer. Single-stranded miRNAs bind to complementary sequences in mRNA thereby inhibiting translation. Over 100 miRNA species have been found in Arabidopsis thaliana, of which some 16 are similar to species characterized from animals. They exhibit diverse developmental and tissue-specific expression profiles and are involved in a wide range of gene regulatory processes.

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