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Nova proteins shuttle between the nucleus and cytoplasm. (A) IMR32 and COS7 cells were fused with PEG 3350, and anti-hnRNPC1 and anti-Nova antibodies were used to detect endogenous proteins. In this field one cell has been fused with COS7 (top; see phase contrast, right panel), and two unfused cells are evident (bottom); cell types can be distinguished with DAPI staining (middle panel). Nova proteins were detected in IMR32 and fused COS7 cells (arrowheads), but no signal in isolated COS7 cells. DAPI staining showed IMR32 cells and COS7 cells, respectively. (B) Shuttling of endogenous Nova from SK-N-BE(2) neuroblastoma cells into mouse NIH 3T3 cells; Nova, hnRNP-C12 and DAPI stains are shown as in (A). (C) Schematic of Flag-tagged Nova NLS and NES domains and deletion constructs generated. (D) COS7 cells were transfected with the indicated Flag-Nova1 plasmid constructs and stained with anti-flag antibody to visualize flag-Nova1 (top panels), and DAPI to visualize nuclei (bottom panels). Nova1 can be seen in the cytoplasm in cells transfected with the WT (left panel; arrows) but not in cells transfected with the ΔNES construct (right panel); in contrast the ΔNLS construct is largely excluded from nuclei (middle panel).