Standard protein expression systems, such as E. coli, often fail to produce folded,
monodisperse, or functional eukaryotic proteins (see Small-scale Expression of Proteins in
E. coli). The expression of these proteins is greatly benefited by using a eukaryotic system,
such as mammalian cells, that contains the appropriate folding and posttranslational
machinery. Here, we describe methods for both small-and large-scale transient expression
in mammalian cells using polyethylenimine (PEI). We find this procedure to be more cost …