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Mol. Cell. Biol., Dec 1995, 6746-6753, Vol 15, No. 12
T Gotoh, S Hattori, S Nakamura, H Kitayama, M Noda, Y Takai, K Kaibuchi, H Matsui, O Hatase and H Takahashi
C3G, which was identified as a Crk SH3 domain-binding guanine
nucleotide-releasing factor, shows sequence similarity to CDC25 and Sos
family proteins (S. Tanaka, T. Morishita, Y. Hashimoto, S. Hattori, S.
Nakamura, M. Shibuya, K. Matuoka, T. Takenawa, T. Kurata, K. Nagashima, and
M. Matsuda, Proc. Natl. Acad. Sci. USA 91:3443-3447, 1994). The substrate
specificity of C3G was examined by in vitro and in vivo experiments. C3G
markedly stimulated dissociation of bound GDP from Rap1B but marginally
affected the same reaction of other Ras family proteins (Ha-Ras, N-Ras, and
RalA). C3G also stimulated binding of GTP- gamma S [guanosine
5'-3-O-(thio)triphosphate] to Rap1B. When C3G and Rap1A were expressed in
COS7 cells, marked accumulation of the active GTP-bound form of Rap1A was
observed, while Sos was not effective in the activation of Rap1A. These
results clearly show that C3G is an activator for Rap1. Furthermore,
expression of C3G with a membrane localization signal in a v-Ki-ras
transformant, DT, induced a reversion of the cells to the flat form,
possibly through the activation of endogenous Rap1.
Copyright © 1995, American Society for Microbiology
Identification of Rap1 as a target for the Crk SH3 domain-binding guanine nucleotide-releasing factor C3G
Division of Biochemistry and Cellular Biology, National Institute of Neuroscience, National Center of Neurology and Psychiatry, Tokyo, Japan.
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