Figure 7.

The ectodomain of TβRII is a monomer and dimerizes upon TGF-β1 binding. (A) COS7 cells were transfected with II-SF. 48 h after transfection, they were incubated in starvation medium and labeled with ³⁵S-Express, and the media collected from the cells were concentrated and centrifuged on 5–15% sucrose gradients without detergent (see Materials and Methods). Fractions were immunoprecipitated with α-HA, and immunoprecipitates were analyzed by SDS-PAGE. (B) Unlabeled media from transfected COS7 cells were collected and cross-linked to iodinated TGF-β1, as described under Materials and Methods. Samples were loaded on sucrose gradients and processed as for A. (C) A graphical representation of the quantitation of bands, as for Figs. 1 and 6.