The Son of sevenless (Sos) gene functions in signaling pathways initiated by the sevenless and epidermal growth factor receptor tyrosine kinases. The Sos gene has now been isolated and sequenced. Its product is a 1595-amino acid protein similar to the CDC25 protein in Saccharomyces cerevisiae, a guanine nucleotide exchange factor that activates Ras. These results imply a role for the ras pathway in Drosophila neuronal development.

No abstract

No abstract

The Son of sevenless (Sos) protein functions as a guanine nucleotide transfer factor for Ras and interacts with the receptor tyrosine kinase Sevenless through the protein Drk, a homolog of mammalian Grb2. In vivo structure-function analysis revealed that the amino terminus of Sos was essential for its function in flies. A molecule lacking the amino terminus was a potent dominant negative. In contrast, a Sos fragment lacking the Drk binding sites was functional and its activity was dependent on the presence of the Sevenless receptor. Furthermore, membrane localization of Sos was independent of Drk. A possible role for Drk as an activator of Sos is discussed and a Drk-independent interaction between Sos and Sevenless is proposed that is likely mediated by the pleckstrin homology domain within the amino terminus.