MicroRNAs

MicroRNA, miRNA, is a type of small, regulatory RNA that does not code for protein. Instead it regulates gene expression by inhibiting the translation of messenger RNA, mRNA, into protein.

MicroRNAs are around 22 nucleotides long and are produced through the cleavage of a double-stranded RNA precursor molecule with a hairpin turn. The two strands separate, and one becomes the mature miRNA, which forms a complex with a group of proteins called RISC, RNA-induced silencing complex.

This complex binds to mRNA through complimentary base pairing between the miRNA and specific sequences in the mRNA, typically in the 3-prime untranslated region. This pairing is usually not perfect, but it is enough to inhibit translation, either through cleavage and destruction of the mRNA or by interfering with the translation process itself.

Either way, gene expression is silenced, which is an important type of post-transcriptional regulation. In fact, dysregulation of miRNA is correlated with potentially deadly diseases, such as cancer and heart disease.