Fig. 6. Nuclear export of ETR-3 is leptomycin B (LMB)-sensitive. GFPcETR3 is cytoplasmic in the absence of LMB in untreated (upper right panel) or mock-treated cells (data not shown), but accumulates in the nucleus following one hour of exposure to 1 µM LMB similar to a positive control containing known NLS and LMB-sensitive NES elements (GFP-PK-Vpr). In three experiments the nuclear concentration of GFPcETR3 increased in the presence of LMB, but some GFPcETR3 was retained in the cytoplasm (this result is shown). In a fourth experiment, LMB treatment resulted in an exclusively nuclear localization of GFPcETR3 (data not shown). The extent of nuclear accumulation of GFPcETR3 in each case is comparable to GFP-PK-Vpr. A cytoplasmic fusion protein that does not enter the nucleus (GFP-PK) is not affected by LMB treatment. No differences in viability were observed in LMB-treated versus untreated or mock-treated cells. Scale bar: 10 µm.