The TGF-beta (transforming growth factor-beta)-related signalling prot
eins, including Decapentaplegic (Dpp) in Drosophila and bone morphogen
ic proteins and activin in vertebrates, affect the growth and patterni
ng of a great variety of structures. However, the mechanisms by which
these ligands regulate gene expression are not understood. Activation
of complexes of type I with type II receptors results in the phosphory
lation and nuclear localization of members of the SMAD protein family(
1-9), which are thought to act as co-activators of transcription, perh
aps in conjunction with sequence-specific cofactors(10). Here we show
that the aminoterminal domain of the Drosophila Mothers against dpp pr
otein (Mad), a mediator of Dpp signalling(11-14), possesses a sequence
-specific DNA-binding activity that becomes apparent when carboxy-term
inal residues are removed. Mad binds to and is required for the activa
tion of an enhancer within the vestigial wing-patterning gene in cells
across the entire developing wing blade. Mad also binds to Dpp-respon
se elements in other genes. These results suggest that Dpp signalling
regulates gene expression by activating Mad binding to target gene enh
ancers.