Protein with 2 signals to the mitochondria and ER. Who would win?

Question

Imagine that you have engineered a gene that encodes a protein with two conflicting signals. One signal is for protein import into the mitochondria and one signal is for import into the endoplasmic reticulum. a) Which signal do you predict would “win out”? Explain your answer. b) Where do you expect to find the protein located in cells? Explain your answer.

Answer 1

This is a super interesting question!

I would predict that the signal for the endoplasmic reticulum would "win out". Firstly the role of the ER is protein and lipid synthesis, folding, modification, and transport. Therefore, this is a more likely location of proteins. In addition to this, the Rough ER (the ER studded with ribosomes, ribosomes are the location of translation) can recognize these signals while the protein is still being made. This means the protein gets directed to the ER right away during its production. In contrast, the mitochondria works post-translationally (after the protein is made) in the cell cytoplasm.

Since the ER signal is noticed first, i would expect to find more of the protein here.