Figure 3From: Framework for a Protein OntologySmad2 component of the TGF-beta signaling pathway. Not all protein forms and pathway branches are indicated. The steps shown are preceded by phosphorylation of Smad4, TGF-beta binding to the receptor, and receptor phosphorylation. Step 1: Phosphorylation of Smad2 by TGF beta receptor I. Step 2: Complex formation of Smad2 and Smad4. Step 3: Nuclear import of Smad2:Smad4. Step 4: Binding of Smad2:Smad4 complex coactivator to responsive element.Back to article page