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 (Marshall, 1996). Previous studies have s hown that phosphorylation is required for Raf-1 activation (Dhillon and Kolch, 2002, Chong et al., 2003). Recent work has demonstrated that phosphorylation also regulates the downregulation of Raf (Dougherty et al., 2005) with two sites participating: Ser 301 and Ser 642
