RAF1 INTERACTION WITH CDC25 PHOSPHATASE TIES MITOGENIC SIGNAL-TRANSDUCTION TO CELL-CYCLE ACTIVATION

The Ras and Raf1 proto-oncogenes transduce extracellular signals that promote cell growth. Cdc25 phosphatases activate the cell division cyc le by dephosphorylation of critical threonine and tyrosine residues wi thin the cyclin-dependent kinases. We show here that Cdc25 phosphatase associates with raf1 in somatic mammalian cells and in meiotic frog o ocytes. Furthermore, Cdc25 phosphatase can be activated in vitro in a Raf1-dependent manner. We suggest that activation of the cell cycle by the Ras/Raf1 pathways might be mediated in part by Cdc25.