Figure 3.

Phosphorylation of Mad by activated Tkv. (A) FLAG-tagged Mad was transfected into COS cells with or without Dpp receptors (Punt and Tkv). Cells were then labeled with [³²P]orthophosphate, treated with 300 ng/ml BMP-2 for 1 h, lysed, and subjected to gel electrophoresis followed by analyses with a phosphorimager. The expression level of Mad was monitored by Western blotting. (B) Phosphorylation of Mad by Tkv was examined by Western blotting. Mad was immunoprecpitated with anti-FLAG antibody and immunoblotted with anti-phosphoserine antibody.