Nucleo-Cytoplasmic Exchange

ID #2440

If we were to be asked a question on the exam and we were shown amino acids and we had to choose from a mitochondrial transit sequence, NLS, NES, or a signal peptide how would we do that? A mitochondrial transit sequence is basic rich, a NLS is basic and positive, an NES is leucine rich, and a signal peptide is hydrophobic but no leucines. How would we decide between NLS, NES, and the transit sequence?

You are correct that a mitochondrial transit sequence and an NLS are both rich in basic amino acids. (Positively charged amino acids are basic amino acids). To distinguish between them, a mitochondrial transit sequence is most likely found at the amino terminal end of the protein, whereas the NLS could be found anywhere in the protein sequence. An NES is rich in leucines, so if you see a signal that is rich in leucine residues you should be able to identify it. Signal peptides are hydrophobic, so if you see many hydrophobic residues you should also be able to identify one. 
Remember, you will receive an amino acid table on the exam in case you want to refresh your memory on what the amino acids look like. 

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