Figure 4.

Truncated Smad3 proteins only minimally transactivate the proximal p21 promoter. (A) Schematic representation of human Smad3 and the two truncated forms (Smad3N and Smad3C) used in B. Amino acid numbers, the N-terminal Mad-homology domain 1 (MH1, striped box), the linker domain and the C-terminal Mad-homology domain 2 (MH2, grey box) of these proteins are shown. Asterisks in hSmad3 and 3C denote the conserved C-terminal phosphorylation motif SSXS. (B) Transactivation of the −143/+8 p21 promoter by truncated Smad3 mutants. HepG2 cells were cotransfected with the −143/+8 p21 promoter construct in the absence (−) or presence of the indicated Smad proteins. The activity of the −143/+8 p21 promoter in the absence of Smads was set arbitrarily to 100%.