Interaction with RXR is necessary for NPM-RAR-induced myeloid differentiation blockade..     ///    "To determine the biological significance of NPM-RAR/RXR interaction, we developed two mutants of NPM-RAR that showed markedly diminished ability to bind RXR. "    ///    These results support the hypothesis that RXR interaction is necessary for NPM-RAR-mediated myeloid maturation arrest.     ///    "U937 subclones expressing the NPM-RAR mutants showed significantly less inhibition of vitamin D3/TGFbeta-induced differentiation, compared with NPM-RAR. "    ///    We have previously shown that NPM-RAR is capable of binding to DNA either as a homodimer or heterodimer with RXR. 