Answer:
A)sorting sequence, which typically contains the positively charged amino acids lysine and arginine.
Step-by-step explanation:
Protein sorting refers to the cellular process by which proteins are transported to their corresponding localizations both inside or outside the cell. A nuclear localization sequence (NLS) is a short amino acid signaling sequence that is able to mediate the transport of proteins into the nucleus. The proteins that are 'tagged' by an NLS sequence can pass through the nuclear envelope via nuclear pores. This sequence (NLS) is typically composed of protein motifs consisting of positively charged lysine (Lys) and arginine (Arg) amino acid residues, which are exposed on the protein surface. In consequence, the NLS sequence is recognized by the importin α/β heterodimer receptor, which transports the NLS-tagged protein into the nucleus. It has been shown that the deletion of the NLS sequence disrupts nuclear import, whereas the fusion of non-nuclear proteins with NLS sequences represents a useful strategy to introduce proteins into the nucleus.