Transcriptional activation by the homeodomain protein Distal-less 3

PCR-based methods and mobility shift competition assays were used to determ ine the basic biochemical features of the homeodomain transcription factor Distal-less 3 (Dlx3), including an optimal DNA binding site, the binding co nstant and dissociation rates of this protein. Expression of Dlx3 protein i n either HeLa cells or Xenopus embryos resulted in strong activation of a m odel target gene construct containing three tandem copies of the Dlx3 bindi ng site upstream from the TATA element. In addition, deletion analysis reve aled that transcriptional activation by Dlx3 depends on two subdomains loca ted on either side of the homeobox: removal of either subdomain resulted in complete loss of Dlx3 function. These observations provide new insight reg arding the function of Dlx3 in vertebrate development and tissue differenti ation and also suggest a mechanism for the dominant inheritance pattern of a hereditary disease resulting from mutation of the DLX3 gene in human.