Characterization of the DNA-binding and dimerization properties of the nuclear orphan receptor germ cell nuclear factor

The orphan receptor germ cell nuclear factor (GCNF) is a member of the supe rfamily of nuclear receptors. During development, GCNF exhibits a restricte d brain-specific expression pattern, whereas GCNF expression in the adult i s germ cell specific. Therefore, the receptor may participate in the regula tion of neurogenesis and reproductive functions. No natural GCNF target gen e has yet been identified, but recent data demonstrate specific and high-af finity binding of GCNF either to the direct repeat DNA element AGGTCAAGGTCA (DRO) or to extended half-sites, such as TCAAGGTCA. In this study, we show that murine GCNF (mGCNF) can bind as a homodimer to extended half-sites, t hus describing a novel property within the nuclear receptor superfamily. Ho modimeric binding to extended half-sites requires the presence of a dimeriz ation function within the mGCNF DNA-binding domain (DBD) and a novel dimeri zation surface encompassing the putative helix 3 and the helix 12 region of the mGCNF ligand-binding domain (LBD). In addition, the mGCNF LED has the potential to adopt different conformations with distinct dimerization prope rties. The helix 12 region of the mGCNF LED not only regulates the switch b etween these dimerization conformations but also dictates the DNA-binding b ehavior and transcriptional properties of the different dimerization confor mations. In summary, our findings describe unique DNA-binding and dimerizat ion properties of a nuclear receptor and suggest a novel mechanism that all ows mGCNF to modulate target gene activity.