You have modified the green fluorescent protein (GFP) to carry a nuclear localiz

Question

You have modified the green fluorescent protein (GFP) to carry a nuclear localization signal at its N-terminus and a nuclear export signal at its C-terminus. When this protein is expressed in cells, you find that about 60% of it is located in the nucleus and the rest in the cytoplasm and that its rates of import and export determine the observed distribution. Nevertheless, you are concerned that the modified GFP might not fold properly even though it retains its fluorescent properties. Specifically, you worry that the 40% in the cytoplasm is not being transported at all because neither signal is exposed, and the 60% in the nucleus has only the nuclear import signal available. To test this, you may treat cells with leptomycin B, a drug that inhibits nuclear export. How might addition of leptomycin B to such cells resolve this issue?

Explanation / Answer

Leptomycin B is an antibiotic with anti-fungal and anti-tumor activity that was first discovered and purified from the fermentation broth and mycelia of Streptomyces. Recently, this antibiotic has become an important tool for studying nuclear localization and trafficking in eukaryotic cells, due to specific inhibition of the CRM1/exportin1 nuclear export pathway, (Ned Watson). Addition of Leptomycin B to such cells should resolve this issue as it will lead to inhibition of the CRM1/exportin1 nuclear export pathway as reported by recent researches of; (Ned Watson) and hence confirm the claim.

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