Evidence for the coidentification of GAP-43, a growth-associated protein, and F1, a plasticity-associated protein

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Abstract
GAP-43 is a fast-axonally transported protein whose expression correlates with periods of axon growth both during development and during regeneration. Similarities in molecular weight (43–47 kDa), pI (4.3–4.5), and aberrant behavior in acrylamide gels suggested that GAP- 43 might be related or identical to protein F1, a protein kinase C substrate that has been shown to undergo a change in phosphorylation state during long-term potentiation in the hippocampus. Here we show that GAP-43 and protein F1 comigrate by two-dimensional PAGE and that antiserum raised against GAP-43 specifically immunoprecipitates protein F1. More direct evidence that GAP-43 and protein F1 are identical proteins was obtained by performing S. aureus V8 protease digests of a mixture of purified 32P-labeled protein F1 and purified GAP-43. Under these conditions, 2 phosphorylated peptide fragments of protein F1 corresponded exactly to 2 Coomassie-stainable bands from purified GAP- 43. We conclude on the basis of these data that GAP-43 and protein F1 are identical proteins. Using light-microscopic immunocytochemistry, we also show that GAP-43/protein F1 immunoreactivity is localized to neuropil areas of the hippocampus consistent with its roles as a protein kinase C substrate in vivo and in long-term potentiation. These findings suggest that nerve growth during development and regeneration, and synaptic plasticity in the adult mammalian brain, may be mediated by a common mechanism involving the phosphorylation of GAP-43/protein F1.

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