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Figure 1. Elements of tyrosine kinase receptor signal transduction pathways showing the role of Sos1. Ligand (L) binds to tyrosine kinase receptor (R), leading to phosphorylations in the cytoplasmic domain of the receptor (p). This recruits adapter proteins (Grb2 and Shc) and Sos1. Bound Sos1 then catalyzes the substitution of GTP for GDP on plasma-membrane-bound Ras proteins. Active GTP/Ras then activates protein kinases, ultimately resulting in activation and translocation of transcription factors to the nucleus, and regulation of transcription of specific target genes.
