title: Expression of Rous sarcoma virus transforming protein pp60v-src in Saccharomyces cerevisiae cells.
abstract: The Rous sarcoma virus (RSV) pp60v-src protein was expressed in Saccharomyces cerevisiae cells either from a plasmid vector carrying the v-src gene or in yeast cells containing a single-copy v-src gene chromosomally integrated. In both yeast strains, v-src gene transcription is regulated by the galactose-inducible GAL10 promoter. Growth in galactose-containing medium resulted in constitutive expression of pp60v-src in the integrated strain and transient expression of higher levels of pp60v-src in the plasmid-bearing strain. The concentration of pp60v-src in the plasmid-bearing strain at its peak of expression was approximately threefold lower than that found in RSV-transformed mammalian cells. pp60v-src synthesized in yeast cells was phosphorylated in vivo on sites within the amino and carboxyl halves of the molecule. In immune complex kinase assays, the yeast pp60v-src was autophosphorylated on tyrosine and was able to phosphorylate exogenous substrates such as casein and enolase. The specific activity of pp60v-src synthesized in yeast cells was approximately 5- to 10-fold higher than that made in mammalian cells. Induction of pp60v-src caused the death of the plasmid-bearing yeast strain and transient inhibition of growth of the single-copy strain. Concomitantly, this induction resulted in high levels of tyrosine phosphorylation of yeast cell proteins. This indicates that pp60v-src functions as a tyrosine-specific phosphotransferase in yeast cells and suggests that hyperphosphorylation of yeast proteins is inimical to cell growth.
mesh_terms: D001358:Avian Sarcoma Viruses / Q000201:enzymology / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics; D005796:Genes; D005814:Genes, Viral; D007700:Kinetics; D015688:Oncogene Protein pp60(v-src); D010766:Phosphorylation; D010957:Plasmids; D014176:Protein Biosynthesis; D011494:Protein Kinases / Q000235:genetics*; D012191:Retroviridae Proteins / Q000235:genetics*; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000254:growth & development; D014158:Transcription, Genetic
chemical_list: D012191:Retroviridae Proteins; D011494:Protein Kinases; D015688:Oncogene Protein pp60(v-src)