The Identification of nuclear localization signals

Nucleoplasmin

When injected into Xenopus laevis oocytes, this protein is transported to the nucleus. 

However, when the protein is treated with a protease that cleaves its tail domain, the core domain remains in the cytoplasm and only the tails localize to the nucleus.

Assay to Determine whether cytosolic factors are required for nuclear transport

Adams, et al., 1990:  

Performed in vitro assay using mammalian cells permeabilized by digitonin

A fluorescent protein to be imported was added to the cells, which were depleted of soluble cytoplasmic components.

It was observed that import of the fluorescently labeled protein required the addition of cytosolic components.

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