The role of the Src homology-2 domain in the lethal effect of Src expression in the yeast Saccharomyces cerevisiae.

Expression of the retroviral transforming gene v-src arrests the proliferation of the yeast Saccharomyces cerevisiae. A functional Src SH2 (Src homology 2) domain is required for this arrest. To examine the mechanism by which Src blocks yeast cell proliferation, and to determine the role of the Src SH2 domain in the growth arrest, src variants were expressed in yeast under the control of the galactose-inducible GAL1 promoter. Following galactose induction of Src expression, phosphotyrosyl-proteins were isolated by immunoprecipitation with beads coupled to either anti-phosphotyrosine antibody or to a recombinant fusion protein containing the Src SH2 domain. A group of SH2-binding phosphotyrosyl proteins was detected in cells expressing toxic forms of Src, but were not detected in cells expressing non-toxic variants. This group of phosphotyrosyl-proteins represents a minor subset of the proteins phosphorylated by v-Src. The lethality of v-Src and the phosphorylation of SH2-binding proteins were co-ordinately affected by alterations in phosphotyrosine-phosphatase activity. These observations indicate that the lethality of Src is correlated with the phosphorylation of proteins that bind to the Src SH2 domain. The role of the SH2 domain in determining the lethal effects of Src in yeast may be similar to its role in targeting Src to substrates necessary for its biological effects in vertebrate cells.