Jennifer Couzin Rather than smoothly asseMBLing on a genE, the proteins that form a major transcription tool, called RNA polymerase I, collide without sticking and zoom off if their companions are seconds behind schedule. The research, reported on page 1623, is not without critics, who contend that the technology used in the study has not advanced enough to support such a model. But the work reflects an increasingly sophisticated effort to delineate the dance performed by transcription machinery.