Editing Expression vector (section)

===Mammalian===
Mammalian expression vectors offer considerable advantages for the expression of mammalian proteins over bacterial expression systems - proper folding, post-translational modifications, and relevant enzymatic activity. It may also be more desirable than other eukaryotic non-mammalian systems whereby the proteins expressed may not contain the correct glycosylations. It is of particular use in producing membrane-associating proteins that require chaperones for proper folding and stability as well as containing numerous post-translational modifications. The downside, however, is the low yield of product in comparison to prokaryotic vectors as well as the costly nature of the techniques involved. Its complicated technology, and potential contamination with animal viruses of mammalian cell expression have also placed a constraint on its use in large-scale industrial production.<ref name="mammalian">{{cite journal |title=Gene Expression in Mammalian Cells and its Applications|author= Kishwar Hayat Khan |journal= Adv Pharm Bull. |year= 2013 |volume= 3 |issue=2 |pages= 257–263 |pmid=24312845 |pmc=3848218 | doi= 10.5681/apb.2013.042 }}</ref>

Cultured mammalian cell lines such as the [[Chinese hamster ovary cell|Chinese hamster ovary (CHO)]], [[COS cells|COS]], including human cell lines such as [[HEK cell|HEK]] and [[HeLa]] may be used to produce protein. Vectors are [[transfected]] into the cells and the DNA may be integrated into the genome by [[homologous recombination]] in the case of stable transfection, or the cells may be transiently transfected. Examples of mammalian expression vectors include the [[adenoviral]] vectors,<ref>{{cite book |year= 1992 |volume=158 |pages=39–66 |author=Berkner KL |title= Viral Expression Vectors |chapter= Expression of Heterologous Sequences in Adenoviral Vectors |series= Current Topics in Microbiology and Immunology |pmid=1582245 |doi= 10.1007/978-3-642-75608-5_3 |isbn= 978-3-642-75610-8 }}</ref> the pSV and the pCMV series of plasmid vectors, [[vaccinia]] and [[retroviral]] vectors,<ref>{{cite journal |journal=Clin Microbiol Rev |year=1990 |volume= 3 |issue=2|pages= 153–170 |pmc=358149|title=Vaccinia virus vectors: new strategies for producing recombinant vaccines |author=Hruby, DE |pmid=2187593 |doi=10.1128/cmr.3.2.153}}</ref> as well as baculovirus.<ref name="Kost2002">{{cite journal|pmid=11906750|doi=10.1016/S0167-7799(01)01911-4|title=Recombinant baculoviruses as mammalian cell gene-delivery vectors|year=2002|last1=Kost|first1=T|journal=Trends in Biotechnology|volume=20|issue=4|pages=173–180|last2=Condreay|first2=JP}}</ref> The promoters for [[cytomegalovirus]] (CMV) and [[SV40]] are commonly used in mammalian expression vectors to drive gene expression. Non-viral promoter, such as the elongation factor (EF)-1 promoter, is also known.<ref>{{cite journal |journal=Gene |year=1990 |volume=91 |issue=2 |pages=217–23 |title=Use of the human elongation factor 1 alpha promoter as a versatile and efficient expression system |vauthors=Kim DW, Uetsuki T, Kaziro Y, Yamaguchi N, Sugano S |pmid =2210382 |doi=10.1016/0378-1119(90)90091-5}}</ref>