p21^ras: From oncoprotein to signal transducer

This chapter discusses the relevance of mutated ras genes for the development of tumors based on the stage in tumor development at which these mutations occurs and on the observation that mutated ras genes are frequently found in only a subfraction of tumor cells. The functions of the p21 ras gene products in signal transduction are discussed in the chapter. Alterations in genes involved in the regulation of growth and differentiation are considered to be the main cause of cancer. Molecular cancer research aims at identifying the genes that are altered in human tumors and elucidating the function. One of the paradigms of this research is the ras gene family. In the human genome, three different functional ras genes are present, the H-ras gene, the K-ras gene, and the N-ras gene, which is not found in viral genomes. Each of these genes has been isolated from human tumors as a “transforming gene.” Several analyses have revealed that transforming ras genes differed from non-transforming ras genes by the presence of a point mutation at one of a few restrictive positions within the gene.