THE SYNAPTIC PROTEIN UNC-18 IS PHOSPHORYLATED BY PROTEIN-KINASE-C

The C. elegans unc-18 encoded protein UNC-18 is implicated in the inte ractions between synaptic vesicles and presynaptic plasma membrane. To further characterize the neural protein, we investigated the phosphor ylation in vitro of the protein expressed in Spodoptera frugiperda Sj2 1 cells. The UNC-18 protein is selectively phosphorylated by protein k inase C (PKC) but not by casein kinase II and cyclic AMP-dependent pro tein kinase. The presumed phosphorylation sites determined by manual E dman degradation were serine-2, serine-322, threonine-462 and serine-5 15, of which the last is highly conserved as a consensus phosphorylati on site for PKC in Drosophila and the mammalian homologue. Phosphoryla ted UNC-18 extracted from C. elegans was also detected, indicating tha t it has a physiological role in intact nerve terminals. Therefore, th e phosphorylation by PKC may play a physiological role in the regulati on. Copyright (C) 1996 Elsevier Science Ltd