Abstract
Three methyl xanthine inhibitors of adenosine 3′,5′-monophosphate phosphodiesterase-theophylline, aminophylline, and caffeine-lengthen the period of the circadian conidiation rhythm of Neurospora. The effects are seen in wild-type strains and in three mutant strains with genetically altered period lengths. These results suggest the possible involvement of adenosine 3′,5′-monophosphate in the control of circadian rhythmicity.