FAR1 LINKS THE SIGNAL-TRANSDUCTION PATHWAY TO THE CELL-CYCLE MACHINERY IN YEAST

Alpha factor induces arrest of yeast a cells in G1 and transcription o f genes involved in mating. Prior work indicates that FUS3, a member o f the MAP kinase family, and FAR1, whose molecular activity is unknown , contribute to cell cycle arrest by inhibiting G1 cyclins. Here we sh ow that FAR1 is a substrate for FUS3 and that this phosphorylation reg ulates association of FAR1 with CDC28-CLN2 kinase. We show also that F AR1 is phosphorylated in vitro by the CDC28-CLN2 complex and in vivo i n a CDC28-dependent manner. Mutational analysis of FAR1 reveals a corr elation between its ability to associate with CDC28-CLN2 and to arrest the cell cycle. These results suggest that FAR1 protein is the link b etween the signaling pathway and the cell cycle machinery.