As a new graduate student, you have been tasked with studying how multiple local

Question

As a new graduate student, you have been tasked with studying how multiple localization signals affect the localization of proteins in cells. To do this, you have engineered a set of genes that code for a protein that contains two different signal sequences on the same polypeptide. Predict the ultimate localization of a protein that contains the following two signal combinations on the same polypeptide and in 1 sentence, state the molecular reason why your protein will go where you say it will go.

A) ER signal sequence and a Mannose-6-phosphate site

B) ER stop transfer sequence and an NLS

C) Mitochondrial signal sequence and an ER-retention signal sequence

D) Mannose-6-phosphate site and an NLS.

E) NLS and an ER signal sequence on the very last amino acids

Explanation / Answer

A) ER signal sequence and a Mannose-6-phosphate site: Both of the siganl sequences translocate the protein into ER lumen or Cis - Goligi network. This is because the signal sequences attached would cause modification in protein such as glycosylation due to which the protein become functional and this may occur either in ER lumen or golgi complex.

B) ER stop transfer sequence and an NLS: The NLS is the nuclear localization sequence containing basic amino acids in a protein translocate the protein into nucleus and ER stop transfer sequence stops the signal of protein translocation into nucleus.

C) Mitochondrial signal sequence targets the transport of protein into mitochondria but the ER - retention signal sequence stops the transport of protein and retains in ER lumen.

D) Mannose - 6 - phosphate site signal is used to target proteins of lysosomes and NLS is nuclear localization siganl sequences target the proteins into nucleus, therefore the proteins are targeted into nucleus rather into lysosomes because the sugar can be delinked from the protein easily or can be degraded by nuclear enzymes.

E) NLS and an ER signal sequence on the very last amino acids target the proteins into ER rather into nucleus because they are on last amino acids.

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