Visualizing assemblies of the proteins that direct cyanobacterial circadian rhythmsKaiB, though, flips between two different shapes, and is only active when it's in an unstable shape—a situation that until now made crystallization impossible. "We mutated KaiB so that it stayed in its active shape, and when we added KaiA and KaiC they arranged themselves around it as they do at night," LiWang said. "We found the secret sauce that allows us to figure out how the springs and gears go together." They were amazed that they obtained crystals within a day of combining the proteins. They also solved an NMR structure of a complex between the active form of KaiB and the domain of a protein (CikA) that transmits signals to regulate gene expression in cyanobacteria. "It's really remarkable that the cyanobacterial clock is so dependent on this rare state of KaiB," Partch said. "The mechanistic information we're getting out of these structures is allowing us to piece together how the clock manages to keep 24-hour time. We're now looking for similar clues in other circadian timekeeping systems, including our own."