The invention describes amino acid residues of the Smad2 protein which are important for phosphorylation and activity, and Smad2 polypeptide fragments and biologically functional variants thereof. Included and dominant-negative variants of Smad2 and antibodies relating thereto. Also included are nucleic acids which encode such variants. Antibodies which selectively bind pathway-restricted Smad proteins phosphorylated at the C-terminal tail also are provided. Methods and products for using such nucleic acids and polypeptides also are provided.
