Growth Associated Protein 43 (GAP43) is a protein encoded by the GAP43 gene in humans. GAP43 is called a "growth" or "plasticity" protein because it is expressed at high levels in neuronal growth cones during development and axonal regeneration, and it is phosphorylated after long-term potentiation and after learning. GAP43 is a crucial component of the axon and presynaptic terminal. Its null mutation leads to death within days after birth, due to axon pathfinding defects. Synonyms GAP43 is also referred to as: protein F1 neuromodulin neural phosphoprotein B-50 axonal membrane protein GAP-43 calmodulin-binding protein P-57 nerve growth-related peptide GAP43 neuron growth-associated protein 43 Function GAP43, is a nervous tissue-specific cytoplasmic protein that can be attached to the membrane via a dual palmitoylation sequence on cysteines 3 and 4. This sequence targets GAP43 to lipid rafts. It is a major protein kinase C (PKC) substrate and is considered to play a key role in neurite formation, regeneration, and plasticity. The role of GAP-43 in CNS development is not limited to effects on axons: It is also a component of the centrosome, and differentiating neurons that do not express GAP-43 show mislocalization of the centrosome and mitotic spindles, particularly in neurogenic cell divisions. As a consequence, in the cerebellum, the neuronal precursor pool fails to expand normally and the cerebellum is significantly smaller. Several different laboratories studying the same protein, now called GAP43, initially used different names. It was designated F1, then B-50, then GAP43, pp46, and finally neuromodulin, each name reflecting a different function of the same molecule. F1 was localized to synapses, and was increased in its phosphorylation one day after learning. However, F1 was not cAMP kinase dependent. B-50 was regulated by the pituitary peptide ACTH and was associated with grooming behavior. In the case of GAP-43, it was designated as a growth-associated protein because its synthesis was upregulated during axonal regeneration. Pp46 was concentrated in neuronal growth cones and was thus postulated to play an important role in brain development. In the case of neuromodulin, it was shown to bind calmodulin avidly. GAP43, the consensus choice for its designation, is a nervous system-specific protein that is attached to the membrane via a dual palmitoylation sequence on cysteines 3 and 4, though it can exist in the non-bound form in the cytoplasm. This dual sequence enables the association of phosphatidylinositol-4,5-bisphosphate [PI(4,5)P2] or PIP2, with actin, facilitating the latter's polymerization