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The GTPase-activating protein (GAP) has been postulated to function either as a negative regulator or as a possible target protein of Ras in mammalian cells and Xenopus oocytes. Ras must be localized in the plasma membrane of vertebrate cells to function, but GAP is localized in the cytosol. To test whether Ras function depends on a cytosolic factor such as GAP, we microinjected into Xenopus oocytes a form of Saccharomyces cerevisiae RAS1 ([Leu68]RAS1 terminated at residue 185, called [Leu68]RAS1(term.] that lacks the consensus membrane localization site, does not respond to GAP in a GTPase assay, but binds to GAP 100-fold more tightly than [Val12]Ras. [Leu68]RAS1(term.) alone did not stimulate oocyte germinal-vesicle breakdown. Instead, [Leu68]RAS1(term.) was observed to inhibit the action of insulin-like growth factor 1 or microinjected [Val12]Ras but not the action of progesterone as monitored by germinal-vesicle breakdown. Coinjection of purified mammalian GAP with [Leu68]RAS1(term.) reduced the inhibition of [Val12]Ras-stimulated germinal-vesicle breakdown. The results raise the possibility that a cytosolic factor is required for the action of [Val12]Ras in Xenopus oocytes and that this factor is either GAP or another protein with which GAP can compete for binding to [Leu68]RAS1(term.).
J B Gibbs, and
M D Schaber, and
T L Schofield, and
E M Scolnick, and
I S Sigal
January 1991,
Biochemical and biophysical research communications,
J B Gibbs, and
M D Schaber, and
T L Schofield, and
E M Scolnick, and
I S Sigal
May 1999,
FEBS letters,
J B Gibbs, and
M D Schaber, and
T L Schofield, and
E M Scolnick, and
I S Sigal
March 1972,
Journal of cell science,
J B Gibbs, and
M D Schaber, and
T L Schofield, and
E M Scolnick, and
I S Sigal
January 1981,
Reproduction, nutrition, developpement,
J B Gibbs, and
M D Schaber, and
T L Schofield, and
E M Scolnick, and
I S Sigal
February 2017,
Scientific reports,
J B Gibbs, and
M D Schaber, and
T L Schofield, and
E M Scolnick, and
I S Sigal
April 1996,
The International journal of developmental biology,
J B Gibbs, and
M D Schaber, and
T L Schofield, and
E M Scolnick, and
I S Sigal
August 1992,
Proceedings of the National Academy of Sciences of the United States of America,
J B Gibbs, and
M D Schaber, and
T L Schofield, and
E M Scolnick, and
I S Sigal
January 1984,
Development, growth & differentiation,
J B Gibbs, and
M D Schaber, and
T L Schofield, and
E M Scolnick, and
I S Sigal
September 2002,
The Journal of biological chemistry,
J B Gibbs, and
M D Schaber, and
T L Schofield, and
E M Scolnick, and
I S Sigal
January 1982,
Differentiation; research in biological diversity,
