Human RNA genes counted up. (Biology).

A new analysis concludes that 200 to 255 human genes, or nearly 1 percent of all human genes, encode short strands of ribonucleic acid instead of protein as their end product.

Scientists initially discovered several genes encoding these so-called microRNAs in worms and recently unearthed similar genes in people and other mammals (SN: 1/12/02, p. 24). The RNA strands made by these genes seem to regulate the activity of other genes, particularly ones involved in the embryonic development of animals.

Seeking to identify as many such genes in people as possible, Lee P. Lim of Massachusetts Institute of Technology and his colleagues developed computer software that scans DNA sequences for stretches that can produce RNA strands with features characteristic of previously identified microRNA strands. For people, this approach netted 188 candidate genes.

Given the efficiency of this scanning procedure, the researchers estimate in the March 7 Science that no more than 255 microRNA genes exist in total. That makes the microRNA gene family comparable in size to other gene families with a role in regulating gene activity.--J.T.