As an example of the unappreciated power of RNA, consider pseudogenes. Surveys of human DNA have found in it almost equal numbers of genes and pseudogenes--defective copies of functional genes. For decades, pseudogenes have been written off as molecular fossils, the remains of genes that were broken by mutation and abandoned by evolution. But this past May a group of Japanese geneticists led by Shinji Hirotsune of the Saitama Medical School reported their discovery of the first functional pseudogene.

Hirotsune was genetically engineering mice to carry a fruit fly gene called sex-lethal. Most mice did fine with this foreign gene, but in one strain sex-lethal lived up to its name; all the mice died in infancy. Looking closer, the scientists discovered that in those mice sex-lethal happened to get inserted right into the middle of a pseudogene, clobbering it. This pseudogene (named makorin1p1) is a greatly shortened copy of makorin1, an ancient gene that mice share with fruit flies, worms and many other species. Although researchers don't know what makorin1 does, they do know that mice have lots of makorin1 pseudogenes and that none of them can make proteins. But if pseudogenes do nothing, why were these mice dying when they lost one?

For some reason, makorin1--and apparently only makorin1 all but shuts down when its pseudogene pl is knocked out. RNA made from the pseudogene, in other words, controls the expression of the "real" gene whose sequence it mimics, even though the two lie on different chromosomes. There is nothing pseudo about that.