Explanation:

Rough Endoplasmic reticulum is found all across the cell by the density increase  near nucleus  and golgi apparatus.A mammalian host system is the preferred expression platform for producing mammalian proteins that have the most native structure and activity. Mammalian expression is the system of choice for studying the function of a particular protein in the most physiologically relevant environment, because it allows for the highest level of posttranslational processing and functional activity of the protein. It is commonly used for the production of antibodies and therapeutic proteins, as well as for proteins that will be used for human use in functional cell-based assays.