Using short RNA sequences called aptamers, which bind to a small molecule compound with high affinity, researchers have developed a general approach for regulating gene expression at the level of translation. The technique, described in a recent issue of Science (282 :296–298, 1998), entails inserting the complementary DNA for an aptamer into the untranslated region of a gene. The small molecule—a dye that can diffuse easily through cell membranes—can then bind specifically to the aptamer-containing transcripts and prevent ribosomes from translating them. In the absence of the dye, translation of the gene can proceed normally. Michael Green, a researcher in the Howard Hughes Medical Institute at the University of Masachusetts Medical Center (Worcester, MA) and the senior author on the study, explains that "this provides a completely independent way of regulating gene expression. It's not just an on-off switch, but you can actually modulate the activity by adjusting the concentration [of the dye]." This flexibility would be useful for studies of gene regulation pathways, and while the approach has only been demonstrated in tissue culture, the team is also hoping to develop it into an inducible gene knock-out system for laboratory animals.