You have isolated the gene for a protein, nuculin, that is normallylocalized to

Question

You have isolated the gene for a protein, nuculin, that is normallylocalized to the nucleus. You locate in the gene the portion of thecoding sequence that codes for the nuclear localization signal(NLS) and engineer it so that a positively charged amino acid inthe signal is replaced by a non-polar amino acid. You then insertthe gene into some cells and observe where the nuculin goes afterits synthesis. What is the effect, if any?
A.) There is no effect. B.) Nuculin moves to the nucleus as it usually does. C.) Nuculin is not moved to the nucleus. D.) Nuculin is not made by the cell at all.
A.) There is no effect. B.) Nuculin moves to the nucleus as it usually does. C.) Nuculin is not moved to the nucleus. D.) Nuculin is not made by the cell at all.

Explanation / Answer

C.) Nuculin is not moved to the nucleus. A nuclear localization signalor sequence (NLS) is anamino acid sequence which acts like a 'tag' on the exposed surfaceof a protein. This sequence is used to target the protein to thecell nucleus through the Nuclear Pore Complex and to direct a newlysynthesized protein into the nucleus via its recognition bycytosolic nuclear transport receptors. Typically, this signalconsists of one or more short sequences of positively chargedlysines or arginines. Different nuclear localized proteins mayshare the same NLS. An NLS has the opposite function of a nuclearexport signal, which targets proteins out of thenucleus.

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