Correct option is D
In this case, we are studying protein trafficking into the endoplasmic reticulum (ER), and it is crucial to verify that the polypeptide is correctly entering the ER. The following experimental controls and conditions provide complementary information to confirm this process:
Condition A involves mixing the cytosol with mRNA coding for a secreted protein and performing western blotting using antibodies against the secreted protein. This step confirms that the protein is present and can be detected in the cytosol.
Condition B includes mixing the cytosol with mRNA for the secreted protein and rough microsomes, followed by western blotting. The presence of rough microsomes, which are part of the ER, allows for observation of the protein trafficking into the ER, as these microsomes can provide the environment for protein insertion into the ER.
Condition C involves adding rough microsomes and mRNA coding for the secreted protein, followed by protease treatment and subsequent western blotting. The protease treatment will degrade any protein that is not successfully translocated into the ER, allowing only those proteins that are correctly inserted into the ER to be detected.
Thus, using A, B, and C together provides a comprehensive control to confirm the entry of the protein into the ER.
