The small GTP-binding protein Rab3A (identical to smg p25A) is expressed in neural/exocrine/endocrine cells, is distributed between the cytosol and secretory vesicle membranes, and may cycle between these locations to regulate exocytosis. It is proposed that the GTP/GDP state of Rab3A controls this distribution. In PC12 cells, cytosolic Rab3A is predominantly GDP- bound, whereas membrane-associated Rab3A is approximately 50% GTP-bound. Two cytosolic factors, GDP dissociation inhibitor (GDI) and guanine nucleotide releasing factor (GRF), act only on GDP · Rab3A, and preferentially with post-translationally modified Rab3A. Rab3A GTPase-activating protein (GAP) does not preferentially act on processed Rab3A, and interacts selectively with GTP · Rab3A. GDI antagonizes GRF but not GAP activity toward Rab3A. These data are consistent with the concept of an ordered Rab3A cycle controlled by factors that regulate the guanine-nucleotide binding state of Rab3A.
|Number of pages||4|
|Journal||Journal of Biological Chemistry|
|Publication status||Published - 1993|
All Science Journal Classification (ASJC) codes
- Molecular Biology
- Cell Biology