Cloning & Expression

Mammalian Expression Vectors for Transient Transfection and Expression

 Mammalian Expression Vectors using CMV Promoters and FLAG® Tag Vectors

What is a CMV promoter? Human cytomegalovirus (CMV) promoter is an expression vector used to drive gene expression. A strong promoter is one of two elements required for active gene expression. It is a region of DNA that controls transcription of a particular gene, which ensures that the expression vector is able to produce enough protein for further downstream assays and analyses.


 CMV, FLAG®, and 3xFLAG® Tag Features

The strong human cytomegalovirus (CMV) promoter regulatory region drives constitutive protein expression levels as high as 1 mg/L in COS cells. For less potent cell lines, protein levels are typically ~0.1 mg/L. The presence of the SV40 replication origin will result in high levels of DNA replication in SV40 replication permissive COS cells. CMV vectors contain the pMB1 (derivative of pBR322) origin for replication in bacterial cells, the b-lactamase gene for ampicillin resistance selection in bacteria, hGH polyA, and the f1 origin.

Vectors containing the preprotrypsin leader (PPT) sequence direct secretion of FLAG® fusion proteins into the culture medium for purification using Anti-FLAG® antibodies, resins, and plates. The 3xFLAG® epitope tag is 20-200 times more sensitive than the original FLAG® tag. In cases of low-level expression, 3xFLAG® is ideal. 3xFLAG® is only 22 amino acids and is therefore unlikely to alter protein function or block other binding sites or epitopes. Like the original FLAG® tag, 3xFLAG® is very hydrophilic and can be cleaved with enterokinase.

Discover more about FLAG® tag technology and browse our complete list of FLAG® and 3xFLAG® vectors, as well as our Anti-FLAG® antibody products.


 Enterokinase Removal of FLAG® Tags and MAT™ Tag Technology

The recognition sequence for enterokinase, Asp-Asp-Asp-Asp-Lys, is found at the C-terminal end of the FLAG® epitope tag. Removal of the FLAG® epitope is possible in all fusion proteins containing an N-terminal FLAG® sequence. Dual tag fusion proteins may also be cleaved with enterokinase for removal of one or more tags, depending on the position of FLAG® epitope in the protein sequence.

The MAT™ tag, or Metal Affinity Tag (HNHRHKH), has been created for purification of recombinant MAT™ fusion proteins using HIS-Select Nickel and Cobalt Affinity Gels. HIS-Select products allow for highly selective purification of histidine-tagged fusion proteins such as MAT™ fusions. Many of our vectors make use of the MAT™ tag, often in combination with the well-known FLAG® tag. MAT™ tag containing vectors are offered in formats for N-terminal or C-terminal tagging.  


 CMV, MAT™ Tag and FLAG® Tag Vector Selection Guide

Our CMV promoter-based vectors provide flexibility in transient or stable expression, cytoplasmic expression or secretion, and N-terminal or C-terminal tagging in various combinations of FLAG® tag, 3xFLAG® tag, c-myc or MAT™ tag. These fusion proteins allow easy detection, purification and analysis of recombinant protein for a wide range of applications.

Vector Selection Guide


Mammalian Expression Vectors for Transient Expression
  Tag Location Tag Cat. No. MCS Region
Cytoplasmic Expression
Dual Tag N,C-Terminal FLAG® and MAT™ C5864
Dual Tag C-Terminal FLAG® and MAT™ C6114
Single Tag N-Terminal FLAG® E7029 pBICEP-CMV 3


 Complete list of our FLAG® Tag and 3xFLAG® vectors and Anti-FLAG® Antibody Products

Discover more about FLAG® tag technology and browse our complete list of FLAG® and 3xFLAG® vectors, as well as our Anti-FLAG® antibody products.

We also provide BICEP bicistronic expression vectors for transient expression of two targets. Stable expression vectors may also be used for transient expression.

Explore our complete Cloning & Expression portfolio for more information.