Expression of the small tyrosine phosphatase (Stp1) in Saccharomyces cerevisiae: A study on protein tyrosine phosphorylation

Small tyrosine phoshatase 1 (Stpl) is a Schizosaccharomyces pombe low-molec ular-mass phosphotyrosine-phosphatase 50% identical to Saccharomyces cerevi siae Ltp1. in order to investigate the role of Stpl in yeast, a mutant was generated having the characteristic of a dominant negative molecule. Change s in protein tyrosine phosphorylation in S. cerevisiae proteome in response to Stpl or its dominant negative mutant expression were analyzed by high-r esolution two-dimensional (2-D) electrophoresis. The most remarkable result is the modification by phosphorylation on tyrosine of several proteins inv olved in carbohydrate metabolism. Twelve proteins were identified on the ba sis of their positions in the anti-phosphotyrosine immunoblot of the 2-D el ectrophoresis. Ten of these present tyrosyl residues that are within the co nsensus sequence for protein kinase CK2 (casein kinase-2). These data open the possibility for the identification of Stp1 substrates in yeast and prov ide hints about the nature of tyrosine phosphorylating agents in yeast and in other organisms where bona fide tyrosine kinases are lacking.