ABSTRACT
The discovery of H-ras, K-ras, and N-ras genes has been described in the first part of this book. In 1983, the same year that N-ras was discovered, an open reading frame located between the actin and tubulin genes of Saccharomyces cerevisiae was shown to encode a protein, YPT, sharing ∼30% identity with mammalian ras proteins. This YPT protein was first considered as the yeast homolog of mammalian ras, but the RASI and RAS2 genes were soon discovered in S. cerevisiae and shown to encode proteins much more closely related to mammalian ras (see Chapter 7). It was, thus, clear that, at least in yeast, some proteins distantly related to ras were present. One year later the rho genes were discovered, first in Aplysia, then in human, rho proteins also shared ∼30% identity with ras or YPT proteins. This second discovery of a protein distantly related to ras gave additional credit to the idea that ras proteins belonged to a family and the fact that these first two discoveries had been fortuitous strongly suggested that it was a large family. It, thus, seemed reasonable to use more systematic approaches to isolate new members of this family.
