Genetic and Molecular Analysis of Suppressors of Ras Mutations
Annual rept.1 Oct 1996-30 Sep 1999
COLORADO UNIV AT BOULDER
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The goal of this research is to understand the regulation of Ras-mediated signaling in C. elegans vulva development. We describe the identification and characterization of a novel gene, sur-8, that functions to regulate a receptor tyrosine kinase-Ras-MAp kinase- mediated signal transduction pathway during C. elegans vulval development. Mutations in sur-8 were identified as suppressors of an activated let-60 ras mutation. Our genetic analysis indicates that sur plays a positive regulatory role in Ras-mediated signaling, and appears to function downstream of Ras but not downstream of Raf. Although sur-8 mutations by themselves have no effect on normal Ras-mediated signaling, reduction of sur-8 function dramatically enhances mpk-1 MAP kinase and ksr-1 mutations and an increase of sur-8 dosage enhances an activated let- 60 ras mutation. We found that sur-8 encodes a novel protein conserved in mammals that is composed predominantly of leucine-rich repeats. SUR-8 interacts directly with LET-60 Ras, but fails to interact with a putative effector domain mutant, P34G. A structural and functional SUR-8 homologue in humans specifically binds K-Ras and N-Pas but not H-Ras in vitro. Our results indicate that sur-8 is an evolutionarily conserved positive regulator of Ras signaling pathways and that SUR-8 may mediate its effects through Ras binding. We also describe evidence that a regulatory B subunit of Protein Phosphatase 2A pP2A positively regulates an RTK-Ras-MAP kinase signaling cascade during Caenorhabditis elegans vulval induction. Although reduction of sur-6 PP2A-B function causes few vulva induction defects in an otherwise wild-type background, sur-6 PP2A-B mutations suppress the Multivulva phenotype of an activated ras mutation and enhance the Vulvaless phenotype of mutations in lin-45 raf sur-8 or mpk-1.
- Genetic Engineering and Molecular Biology
- Anatomy and Physiology