Figure 3

Smad1 interacts with the pre-assembled HsN3 and BMP type I receptor activation enhances the interaction. A. The prosequence-containing form (pre-assembled form) of HsN3 interacts with Smad1 or the MH2 domain of Smad1 (Smad1C) in COS cells upon co-expression. COS cells were transiently transfected with the indicated plasmids and metabolically labeled with ³⁵S-methionine for the last 4 hrs. Cell lysates were immunoprecipitated with either anti-Flag to detect HsN3 (left panel) or with anti-T7 to detect Smad1 and Smad1C (right panel). The co-precipitated prosequence-containing HsN3 in both panels is marked by a filled arrow and labeled as "Pro-N3-F" and a cartoon symbol shown in Fig. 2A. The mature HsN3 is marked by an open arrow and labeled by a cartoon symbol with the cleaved prosequence next to the mature HsN3. B. The activation of BMP type I receptor ALK3 enhances the interaction between Smad1 and the pre-assembled HsN3. Methods are same as in Fig. 2C.