PHOSPHORYLATION OF RABPHILIN-3A, A PUTATIVE TARGET PROTEIN FOR RAB3A,BY CYCLIC-AMP-DEPENDENT PROTEIN-KINASE

Rab3A small GTP-binding protein and its associated proteins, such as R abphilin-3A, a putative target protein for Rab3A, MSS4, a stimulatory GDP/GTP exchange protein for Rab3A, and Rab GDI, a translocator for th e Rab family members including Rab3A, are implicated in neurotransmitt er release. We have investigated here the phosphorylation of these pro teins by cyclic AMP-dependent protein kinase (protein kinase A). Neith er Rab3A, MSS4, nor Rab GDI was phosphorylated, but Rabphilin-3A was p hosphorylated at its N-terminal region. About 0.8 mol of phosphate was maximally incorporated into one mol of Rabphilin-3A. These results su ggest that Rabphilin-3A is one of the targets for protein kinase A whi ch modulates neurotransmitter release. (C) 1994 Academic Press, Inc.