DNA usually grabs the headlines for its starring role as the archive of genetic information. But many of the really difficult operations that a cell performs are carried out by RNA, DNA's close chemical cousin. So deeply has RNA been overshadowed that two of its major roles in the cell have come to light only in the last few years. One, a way of fine-tuning the activity of genes, has been the subject of a flurry of recent reports documenting RNA's part in central operations like stem cells, cell differentiation, insulin production and cancer. In its fine-tuning role, RNA is...