Mechanism of activation of the Caenorhabditis elegans ras homologue let-60 by a novel, temperature-sensitive, gain-of-function mutation

Genetics. 1997 Jun;146(2):553-65. doi: 10.1093/genetics/146.2.553.

Abstract

The Caenorhabditis elegans let-60 gene encodes a Ras protein that mediates induction of the hermaphrodite vulva. To better understand how mutations constitutively activate Ras and cause unregulated cell division, we have characterized ga89, a temperature-sensitive, gain-of-function mutation in let-60 ras. At 25 degrees, ga89 increases let-60 activity resulting in a multivulva phenotype. At 15 degrees, ga89 decreases let-60 activity resulting in a vulvaless phenotype in let-60(ga89)/Df animals. The ga89 mutation causes a leucine (L) to phenylalanine (F) substitution at amino acid 19, a residue conserved in all Ras proteins. We introduced the L19F change into human H-Ras protein and found that the in vitro GTPase activity of H-Ras became temperature-dependent. Genetic experiments suggest that LET-60 (L19F) interacts with GAP and GNEF, since mutations that decrease GAP and GNEF activity affect the multivulva phenotype of let-60(ga89) animals. These results suggest that the L19F mutation primarily affects the intrinsic rate of GTP hydrolysis by Ras, and that this effect may be sufficient to account for the activated-Ras phenotype caused by let-60(ga89). Our results suggest that a mutation in a human ras gene analogous to ga89 might contribute to oncogenic transformation.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Caenorhabditis elegans / genetics*
  • Caenorhabditis elegans / growth & development
  • Caenorhabditis elegans / metabolism
  • Caenorhabditis elegans Proteins*
  • Cell Differentiation / genetics
  • Cell Division
  • Female
  • GTP Phosphohydrolases / genetics
  • GTP Phosphohydrolases / metabolism
  • GTPase-Activating Proteins
  • Gene Expression Regulation, Developmental*
  • Genes, ras
  • Guanine Nucleotide Exchange Factors
  • Helminth Proteins / genetics*
  • Helminth Proteins / metabolism
  • Humans
  • Mutation
  • Phenotype
  • Proteins / metabolism
  • Signal Transduction
  • Temperature
  • Vulva / growth & development
  • ras GTPase-Activating Proteins
  • ras Guanine Nucleotide Exchange Factors
  • ras Proteins / genetics
  • ras Proteins / metabolism

Substances

  • Caenorhabditis elegans Proteins
  • GTPase-Activating Proteins
  • Guanine Nucleotide Exchange Factors
  • Helminth Proteins
  • Proteins
  • ras GTPase-Activating Proteins
  • ras Guanine Nucleotide Exchange Factors
  • let-60 protein, C elegans
  • GTP Phosphohydrolases
  • ras Proteins