The aminoterminus of c-Raf-1 binds a 28-kD cellular protein.

The regulatory aminoterminal domain of c-Raf-1 expressed as glutathione S-transferase fusion protein associates with a 28-kD cellular protein after treatment with lysates from A431 cells. Both proteins become phosphorylated in vitro by an unidentified cellular protein kinase also present in the complex. The association of the 28-kD protein depends on Cys 168 and Ser 259, suggesting that two independent epitopes of c-Raf-1 are required for binding.