Kinase suppressor of Ras (KSR) is a loss-of-function allele that suppresses the rough eye
phenotype of activated Ras in Drosophila and the multivulval phenotype of activated Ras in
Caenorhabditis elegans. Genetic and biochemical studies suggest that KSR is a positive
regulator of Ras signaling that functions between Ras and Raf or in a pathway parallel to
Raf. We examined the effect of mammalian KSR expression on the activation of extracellular
ligand-regulated (ERK) mitogen-activated protein (MAP) kinase in fibroblasts. Ectopic …