Fig. 5. Schematic representation of the role of PKR in PDGF signaling. PKR and Stat3 are constitutively associated with the PDGF β-receptor. PKR is required for both serine and tyrosine phosphorylation of Stat3 in response to PDGF. The interaction of PKR and Stat3 on the PDGF β-receptor may be a part of a large complex involving additional factors not shown in the model. The open, hatched and striped molecules represent PKR, Stat3 and Stat1 proteins, respectively.