Direct interaction of two homeoproteins, Homothorax and Extradenticle, is essential for EXD nuclear localization and function

The Drosophila Homothorax (HTH) and Extradenticle (EXD) are two homeoprotei ns required in a number of developmental processes. EXD can function as a c ofactor to Hox proteins. Its nuclear localization is dependent on HTH. In t his study we present evidence of in vivo physical interaction between HTH a nd EXD, mediated primarily through an evolutionarily conserved MH domain in HTH, This interaction is essential for the mutual stabilization of both pr oteins, for EXD nuclear localization, and for the cooperative DNA binding o f the EXD-HTH heterodimer. Some in vivo functions require both EXD and HTH in the nucleus, suggesting that the EXD-HTH complex may function as a trans criptional regulator. (C) 2000 Elsevier Science Ireland Ltd. All rights res erved.