In the UK, EPCC is working with biologists to investigate the mechanisms behind biological clocks. Many different organisms – bacteria, plants, animals – use an internal clock to regulate aspects of their behavior to occur at certain times of the day or night. These are circadian rhythms: examples include sleep in humans and photosynthesis in plants. Such circadian rhythms are influenced by environmental cues, such as the natural cycle of sunrise and sunset. If these cues are removed or disrupted the circadian clock takes a certain amount of time to adjust, for example jet-lag following a rapid change in time zones. Professor Andrew Millar and his colleagues at the Centre for Systems Biology at the University of Edinburgh in Scotland use a combination of experiment and computer modelling to investigate the molecular mechanism behind circadian clocks. EPCC has recently joined the modelling work, reflecting the increasing demand in the biological sciences for high-performance computing to tackle complex problems. The genetic underpinnings of circadian rhythms are not fully understood. However, as the same mechanism appears to have evolved on a number of different occasions, it is clearly very important. The ability to combine experiment, where the action of individual genes can be assessed, and modelling, where a large number of possible model mechanisms can be evaluated quickly, provides a powerful tool to investigate these biological clocks. The team currently uses the IBM Blue Gene/L machine at the University of Edinburgh to perform large-scale calculations. Centre for Systems Biology: http://csbe.bio.ed.ac.uk