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 cycle by dephosphorylation of critical threonine and tyrosine residues within the cyclin-dependent kinases. We show here that Cdc25 phosphatase associates with raf1 in somatic mammalian cells and in meiotic frog oocytes. 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.