THE CRY(B) MUTATION IDENTIFIES CRYPTOCHROME AS A CIRCADIAN PHOTORECEPTOR IN DROSOPHILA

A new rhythm mutation was isolated based on its elimination of per-con trolled luciferase cycling. Levels of period or timeless clock gene pr oducts in the mutant are flat in daily light-dark cycles or constant d arkness (although PER and TIM oscillate normally in temperature cycles ). Consistent with the fact that light normally suppresses TIM, cry(b) is an apparent null mutation in a gene encoding Drosophila's version of the blue light receptor cryptochrome. Behaviorally cry(b) exhibits poor synchronization to light-dark cycles in genetic backgrounds that cause external blindness or demand several hours of daily rhythm reset s, and it shows no response to brief light pulses. cry(b) flies are rh ythmic in constant darkness, correlating with robust PER and TIM cycli ng in certain pacemaker neurons.