What are the features of mammalian expression system?

Mammalian expression system is generally more difficult to work with than the bacterial one, which usually takes longer time to express protein of interest, has lower yield, and is often more expensive. Despite of these shortcomings, mammalian expression system offers considerable advantages for the expression of mammalian proteins and membrane-associating proteins because of its capability in proper folding and correct post-translational modifications. Proteins expressed in mammalian cells are nearly the same with the natural proteins in terms of structure, glycosylation, and can be assembled into multi-subunit protein, facilitating a high biological/enzymatic activity.