FUNCTIONAL AND GENETIC-CHARACTERIZATION OF THE OLIGOMERIZATION AND DNA-BINDING PROPERTIES OF THE DROSOPHILA DOUBLESEX PROTEINS

The doublesex (dsx) gene of Drosophila melanogaster encodes both male- specific (DSXM) and female-specific (DSXF) polypeptides, which are req uired for normal differentiation of numerous sexually dimorphic somati c traits. The DSX polypeptides are transcription factors and have been shown previously to bind through a zinc finger-like domain to specifi c sites in an enhancer regulating sex-specific expression of yolk prot ein genes. We have determined the consensus target sequence for this D NA binding domain to be a palindromic sequence (G)(A)NNAC(T)(A)A(A)(T) GTNN(T)(C) composed of two half-sites around a central (A/T) base pair . its predicted by the symmetric nature of this site, we have found th at the DSX proteins exist as dimers in vivo and have mapped two indepe ndent dimerization domains by the yeast two-hybrid method; one in the non-sex-specific amino-terminal region of the protein and one that inc ludes the partially sex-specific carboxy-terminal domains of both the male and female polypeptides. We have further identified a missense mu tation that eliminates dsx function in female flies, and shown that th e same mutation prevents dimerization of DSXF in the yeast two-hybrid system, indicating a critical role for dimerization in dsx function in vivo.