Imagine you have engineered a set of genes, each encoding a protein with a pair

Question

Imagine you have engineered a set of genes, each encoding a protein with a pair of conflicting signal sequences that specify different compartments. If the genes were expressed in a cell, predict which signal would win out for the following combinations. Explain your reasoning. If you don’t think it is possible to predict the result, say so and explain why.

A. Signals for import into the mitochondria and import into ER.

B. Signals for import into the nucleus and retention in ER.

C. Signals for import into the nucleus and import into the chloroplast.

Explanation / Answer

In both A and B cases, the ERsignal would win

(A and B) Obviously, the protein will get to the ER as the signal need to get import into the ER will be seen located at the N-terminus of the protein. This signal will work even before you have the internal signal for nuclear import is synthesized.

But one thing is there, once the protein will enter the ER, you cannot expect the signal sequence for nuclear import to function as it will not have a chance to interact with cytosolic nuclear import receptors.

(C)

In case of C, both signals will win, as the proteins will be produced in the free floating ribosomes and using the signal, the protein will be taken to nucleus and chloroplast.

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