Figure 1.

Modular structure of Raf. The Raf isoforms Raf-1, A-Raf and B-Raf share three conserved domains termed CR1, CR2 and CR3. CR1 contains a Ras-binding subdomain and a cysteine-rich subdomain, both required to bind to activated Ras (Ras-GTP) at the cell membrane. CR2 is rich in serine and threonine residues and negatively regulates the biological activity of the catalytic domain. This domain binds also regulatory 14-3-3 proteins. CR3 encompasses the protein kinase domain.