In the last grant period this lab helped to elucidate key features of a signal transduction pathway which appears to be important for growth factor signalling and differentiation in mammalian cells as well as development in less complex organisms. This pathway extends from a diverse group of membrane receptors through p21ras to Raf-1 to Map kinase kinase (MEK), to Map kinase and then to transcription factors in athe nucleus. In this grant period, we will attempt to extend our understanding of this critical signal transduction pathway. Novel substrates for both Raf-1 an MEK will be identified. In addition we will use the context of the program to attempt to see if the molecules in this pathway play a role in mammalian development as they already known to do in the development of simpler organisms.