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Ras GTPase-Activating Protein: A Substrate and a Potential Binding Protein of the Protein-Tyrosine Kinase p56lck

Kurt E. Amrein, Nicholas Flint, Barbel Panholzer and Paul Burn
Proceedings of the National Academy of Sciences of the United States of America
Vol. 89, No. 8 (Apr. 15, 1992), pp. 3343-3346
Stable URL: http://www.jstor.org/stable/2359095
Page Count: 4
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Ras GTPase-Activating Protein: A Substrate and a Potential Binding Protein of the Protein-Tyrosine Kinase p56lck
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Abstract

Ras GTPase-activating protein (GAP) is a cytoplasmic factor that regulates the GTPase activity of p21ras. Phosphorylation of GAP on tyrosine has recently been reported by several groups and may be an important step in linking signaling pathways involving p21ras and protein-tyrosine kinases. p56lck, a src-like protein-tyrosine kinase, seems to play a crucial role in T-cell development and T-cell activation. However, the molecular mechanisms of T-cell signaling involving p56lck and the substrates of p56lck have not yet been identified. To test whether GAP is a substrate of p56lck, in vitro kinase reactions were performed with purified, recombinant GAP and p56lck. We found that GAP became specifically phosphorylated on tyrosine within one tryptic peptide. Furthermore, coimmunoprecipitation studies provided evidence that the tyrosine-phosphorylated form of GAP is bound to p56lck. These results suggest that in T cells the function of GAP might be regulated through its phosphorylation on tyrosine and binding to the protein-tyrosine kinase p56lck.

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