FHX, a novel fork head factor with a dual DNA binding specificity

The HNF3/fork head family includes a large number of transcription factors that share a structurally related DNA binding domain. Bork head factors hav e been shown to play important roles both during development and in the adu lt. We now describe the cloning of a novel mammalian fork head factor that we have named FHX ((f) under bar ork head (h) under bar omologous (X) under bar (FHX), which is expressed in many adult tissues. In the embryo, FHX ex pression showed a very early onset during the cleavage stages of preimplant ation development. Polymerase chain reaction-assisted site selection experi ments showed that FHX bound DNA with a dual sequence specificity. Sites rec ognized by FHX could be classified into two different types according to th eir sequences. Binding of FHX to sequences of each type appeared to occur i ndependently, Our data suggest that either different regions of the fork he ad domain or different molecular forms of this domain could be involved in binding of FHX to each type of site. In transfection assays, FHX was capabl e of activating transcription from promoters containing FHX sites of either type.