You have isolated the gene for a protein nuculin a protein t

You have isolated the gene for a protein, nuculin (a protein that some people believe resides in the nuculus) that is normally localized to the nucleus. You locate in the gene the portion of the coding sequence that codes for the nuclear localization signal (NLS) and engineer it so that a positively charged amino acid in the signal is replaced by a nonpolar amino acid) You then insert the gene into some cells and observe where nuculin goes after its synthesis. What is the effect, if any? There is no effect. Nuculin moves to the nucleus as it usually does. Nuculin is not moved to the nucleus. Nuculin is not made by the cell at all.

Solution

C, Nuculin is not moved to the nucleus

The signal sequence that permits entry to the nucleus is called nuclear localization signal NLS. These sequences are very small generally 10 aminoacids in length and tags a protein for import into the nucleus by nuclear transport. Nuclear Localization signal consists of one or more short sequences of positively charged lysines or arginines exposed on the protein surface.

So, here as we have replaced the positively charged amino acid by a non-polar aminoacid, Nuculin cannot be imported into the nucleus,as it cannot be binded with the importin(protein - importin complex only enters into the nucleus by nuclear pore).