Abstract
Protein IV from synaptosomal fractions of Drosophila heads is phosphorylated in vitro by an endogenous cyclic adenosine monophosphate (cAMP)-dependent protein kinase. The in vivo phosphorylation of this protein is affected by light. Two visual mutants, tan and stoned, exhibit altered levels of in vivo phosphorylation of protein IV. The tan strain shows depressed in vivo levels of phosphorylation of protein IV, whereas stoned shows an increase in the in vivo level of phosphorylation of this same protein. Protein D is phosphorylated in vitro by an endogenous Ca2+/calmodulin-dependent protein kinase and has a molecular weight identical to that of protein IV. The stoned mutant strain shows an increase in the in vivo level of phosphorylation of protein D. The data presented here suggest that the phosphorylation of protein IV, and perhaps D, may play a role in the early processing of visual information in the fly.