Functional domains of the NPM protein and structure of the NPM-RAR and reciprocal RAR-NPM proteins generated in t(5;17)-APL. A relatively short N-terminal portion of NPM containing the oligomerization domain of the protein is linked to RAR. In the index patient, a longer form of the fusion protein was identified, containing an additional sequences of uncertain origin. The reciprocal RAR-NPM protein could potentially interact with wild-type NPM and interfere with NPM functions.