The t(5;17) acute promyelocytic leukemia fusion protein NPM-RAR interacts with co-repressor and co-activator proteins and exhibits both positive and negative transcriptional properties..     ///    "In addition, NPM-RAR decreases basal transcription from some promoters and acts in a dominant-negative fashion when co-transfected with wild-type RARalpha. "    ///    Two NPM-RAR molecules are expressed as a result of alternative RNA splicing.     ///    Both NPM-RAR and PML-RAR interact with the co-repressor protein SMRTe in a manner that is less sensitive than RARalpha to dissociation by retinoic acid.     ///    "The level of transactivation induced by the NPM-RAR fusions differs from the level of transactivation induced by wild-type RARalpha in both a promoter and cell specific fashion, and more closely parallels the pattern of activation of the PML-RAR fusion than wild-type RARalpha. "    ///    "These data indicate that the NPM-RAR fusion proteins can modulate expression of retinoid-responsive genes in a positive or negative manner, depending on context of the promoter, and lend support to the hypothesis that aberrant transcriptional activation underlies the APL phenotype. "    ///    The NPM-RAR fusion proteins bind to retinoic acid response element sequences as either homodimers or as heterodimers with RXR. 