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 proli feration of the yeast Saccharomyces cerevisiae. A functional Src SH2 ( Src homology 2) domain is required for this arrest, To examine the mec hanism 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, phosphotyro syl-proteins were isolated by immunoprecipitation with beads coupled t o either anti-phosphotyrosine antibody or to a recombinant fusion prot ein containing the Src SH2 domain, A group of SH2-binding phosphotyros yl-proteins was detected in cells expressing toxic forms of Src, but w ere not detected in cells expressing nan-toxic variants, This group of phosphotyrosyl-proteins represents a minor subset of the proteins pho sphorylated by v-Src, The lethality of v-Src and the phosphorylation o f SH2-binding proteins were co-ordinately affected by alterations in p hosphotyrosine-phosphatase activity. These observations indicate that the lethality of Src is correlated with the phosphorylation of protein s that bind to the Src SH2 domain, The role of the SH2 domain in deter mining the lethal effects of Src in yeast may be similar to its role i n targeting Src to substrates necessary for its biological effects in vertebrate cells. (C) 1997 Published by Elsevier Science Ltd.