The protein encoded by this gene binds proteins of the TEA domain family of transcription factors (TEFs) through the Vg (vestigial) homology region found in its N-terminus. It may thus function as a specific coactivator for the mammalian TEFs. TDU interacted directly with the TEA domain family member, TEF1, and deletion of the Vg homology region abolished the interaction. The TDU-TEF1 dimer activated a reporter plasmid, and expression of TDU in Drosophila rescued loss of Vg function. The interaction was stronger in cardiac myocytes, suggesting a myocyte-specific factor may participate in the interaction. Vgll1 was weakly active in driving expression of a reporter gene from the mouse skeletal muscle alpha-actin promoter, and Vgll1 could partially reverse the inhibitory effect of TEF1 in this assay.