Heterogeneous nuclear ribonucleoprotein (hnRNP) D⁄AUF1 functions in mRNA genesis in the nucleus and modulates mRNA decay in the cyto-plasm. Although it is primarily nuclear, it shuttles between the nucleus and cytoplasm. We studied the nuclear import and export of the last exon-enco-ding sequence common to all its isoforms by its expression as a green fluor-escent protein-fusion protein in HeLa cells and by heterokaryon assay.