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A dominant activating mutation in the effector region of RAS abolishes IRA2 sensitivity
1Department of Biochemistry and Molecular Biology, University of Chicago, Illinois 60637.
Abstract:
Previously described mutations in RAS genes that cause a dominant activated phenotype affect the intrinsic biochemical properties of RAS proteins, either decreasing the intrinsic GTPase or reducing the affinity for guanine nucleotides. In this report, we describe a novel activating mutation in the RAS2 gene of Saccharomyces cerevisiae that does not alter intrinsic biochemical properties of the mutant RAS2 protein. Rather, this mutation, RAS2-P41S (proline 41 to serine), which lies in the effector region of RAS, is shown to abolish the ability of the IRA2 protein to stimulate the GTPase activity of the mutant RAS protein. This mutation also modestly reduced the ability of the mutant protein to stimulate the target adenylate cyclase in an in vitro assay, although in vivo the phenotypes it induced suggest that it retains potency in stimulation of adenylate cyclase. Our results demonstrate that although the effector region of RAS appears to be important for interaction with both target effector and negative regulators of RAS, it is possible to eliminate negative regulator responsiveness and retain potency in effector stimulation.
Insights
A novel RAS2 gene mutation in yeast creates an activated RAS protein without altering its biochemistry. This mutation disrupts negative regulation by IRA2, demonstrating a way to uncouple negative regulation while maintaining effector pathway activation.
Area of Science:
- Molecular Biology
- Yeast Genetics
- Signal Transduction
Background:
- RAS proteins are key regulators of cellular signaling pathways.
- Activating mutations in RAS genes typically alter intrinsic GTPase activity or nucleotide binding.
- Understanding RAS regulation is crucial for deciphering cellular processes.
Purpose of the Study:
- To investigate a novel activating mutation in the RAS2 gene of Saccharomyces cerevisiae.
- To characterize the biochemical and functional consequences of the RAS2-P41S mutation.
- To explore the role of the RAS effector region in protein-protein interactions.
Main Methods:
- Site-directed mutagenesis to create the RAS2-P41S mutant.
- Biochemical assays to measure GTPase activity and effector stimulation.
- In vitro and in vivo functional analyses in yeast.
Main Results:
- The RAS2-P41S mutation does not affect the intrinsic biochemical properties of the RAS2 protein.
- RAS2-P41S abolishes IRA2-mediated stimulation of RAS2 GTPase activity.
- The mutation retains, and may even enhance, in vivo stimulation of adenylate cyclase.
Conclusions:
- The effector region of RAS is critical for interaction with both effectors and negative regulators.
- It is possible to generate constitutively active RAS proteins by disrupting negative regulation.
- This provides a new model for understanding RAS signaling and its dysregulation.