The Ras pathway is a critical signal transduction cascade involved in regulating cellular proliferation, differentiation, survival, and oncogenic transformation. Members of the Raf serine/threonine kinase family are key intermediates in this cascade, functioning to relay signals from activated Ras to the downstream protein kinases MEK and ERK. Previous studies have shown that phosphorylation is required for Raf-1 activation. Recent work has demonstrated that phosphorylation also regulates the downregulation of Raf with two sites participating: Ser301 and Ser642.