Light-induced phase shifting of the circadian conidiation rhythm is inhibited by calmodulin antagonists in Neurospora crassa

Abstract

The effects of calmodulin antagonists and inhibitors of protein kinases and phosphatases on light-induced phase shifting were investigated in Neurospora crassa. Calmodulin antagonists, namely, trifluoperazine, chlorpromazine, and W-7, almost completely inhibited the light-induced phase shifting without having any effect on the arcadian clock itself. Chlorpromazine was less effective in inhibiting the light-induced phase shifting than trifluoperazine. W-5, a dechlorinated analogue of W-7, failed to inhibit the light-induced phase shifting at the same concentration as that at which W-7 was effective. These results suggest that calmodulin is required during signal transduction from the light-perceiving system to the circadian clock in N. crassa. Inhibitors of protein phosphorylation did not inhibit the light-induced phase shifting, although these inhibitors completely inhibited mycelial growth. Trifluoperazine partially inhibited the phosphorylation of three proteins when phosphorylation was assayed in vitro.