You are studying the export of this protein from the ER via vesicles. In normal

Question

You are studying the export of this protein from the ER via vesicles.  

In normal cells, this p77 protein is imported into the ER through a protein translocator and folds into its correct shape in the ER lumen.

However, in a mutant strain which you have expertly developed, the mutant protein is imported into the ER lumen but is never exported.

The mutant protein appears to function identically to the normal protein, and in the laboratory, it is as active as its normal counterpart. Which of the following mutations would be most likely to produce the observed results?

(a) An inactivating mutation in the signal peptidase that removes the sorting signal

(b) An inactivating mutation in SRP

(c) An inactivating mutation in the ribosomes  

(d) An inactivating mutation in a chaperone protein

Explain why you chose your answer, and explain why you did NOT choose the others.

Explanation / Answer

Ans -(a). According to the given information mutant protein is already formed properly , targeted to EPR and folded properly as it appears identical to the normal protein . This indicates that there is no mutation in SRP , Ribosomes and chaperon protein. And now if protein is never exported then there must be mutation which cause inactivation of signal peptidase.

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