non-coding RNA

We often picture RNA as a messenger that carries a gene's instructions to be turned into protein. But many RNAs are never translated at all; they are the finished product themselves. A non-coding RNA is a functional RNA molecule that does its job without encoding a protein.

This is a large and varied family. It includes the transfer and ribosomal RNAs essential to protein synthesis, small regulators such as microRNAs that tune gene output, and long non-coding RNAs that can guide chromatin into active or silent states. Some sit at the heart of epigenetic control, for example the RNA that coats an X chromosome during inactivation.

By binding to DNA, other RNAs, or proteins, non-coding RNAs act as scaffolds, guides, and switches in gene regulation. They expanded our picture of the genome, showing that much DNA once dismissed as useless is in fact transcribed into working RNA.

Caution is warranted, though. The genome produces enormous amounts of RNA, and demonstrating that a given non-coding transcript has a real biological function takes careful experiment rather than mere detection.