FUS3 phosphorylates multiple components of the mating signal transduction cascade: evidence for STE12 and FAR1.
The mitogen-activated protein (MAP) kinase homologue FUS3 mediates both transcription and G1 arrest in a pheromone-induced signal transduction cascade in Saccharomyces cerevisiae. We report an in vitro kinase assay for FUS3 and its use in identifying candidate substrates. The assay requires catalytically active FUS3 and pheromone induction. STE7, a MAP kinase kinase homologue, is needed for maximal activity. At least seven proteins that specifically associate with FUS3 are phosphorylated in the assay. Many of these substrates are physiologically relevant and are affected by in vivo levels of numerous signal transduction components. One substrate is likely to be the transcription factor STE12. A second is likely to be FAR1, a protein required for G1 arrest. FAR1 was isolated as a multicopy suppressor of a nonarresting fus3 mutant and interacts with FUS3 in a two hybrid system. Consistent with this FAR1 is a good substrate in vitro and generates a FUS3-associated substrate of expected size. These data support a model in which FUS3 mediates transcription and G1 arrest by direct activation of STE12 and FAR1 and phosphorylates many other proteins involved in the response to pheromone.
Elion
E A
EA
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115.
Satterberg
B
B
Kranz
J E
JE
D001483:Base Sequence; D018797:Cell Cycle Proteins; D050756:Cyclin-Dependent Kinase Inhibitor Proteins; D004591:Electrophoresis, Polyacrylamide Gel; D005656:Fungal Proteins / Q000378:metabolism*; D016193:G1 Phase; D000072235:Mating Factor; D020928:Mitogen-Activated Protein Kinases; D008969:Molecular Sequence Data; D010455:Peptides / Q000494:pharmacology; D010675:Pheromones / Q000494:pharmacology; D010766:Phosphorylation; D010957:Plasmids; D011233:Precipitin Tests; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D012097:Repressor Proteins; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D015398:Signal Transduction; D013489:Suppression, Genetic; D014157:Transcription Factors / Q000378:metabolism*
D018797:Cell Cycle Proteins; D050756:Cyclin-Dependent Kinase Inhibitor Proteins; C081353:FAR1 protein, S cerevisiae; D005656:Fungal Proteins; D010455:Peptides; D010675:Pheromones; D012097:Repressor Proteins; C489241:STE12 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D000072235:Mating Factor; D011505:Protein-Tyrosine Kinases; C075580:FUS3 protein, S cerevisiae; D020928:Mitogen-Activated Protein Kinases