FLAG 和 3xFLAG 標簽：
A Proven System for Detection and Purification of Proteins The FLAG Expression System is an established way to express, purify and detect recombinant fusion proteins. FLAG and 3xFLAG have proven utility in numerous applications such as Western blotting, immunocytochemistry, immunoprecipitation, flow cytometry, protein purification, and in the study of protein-protein interactions, cell ultrastructure and protein localization. These small hydrophilic tags facilitate superior detection and purification of recombinant fusion proteins when using our highly specific and sensitive ANTI-FLAG antibodies. Ideal Epitope Tags: Small, Hydrophilic and Cleavable The FLAG expression system utilizes a short, hydrophilic 8-amino acid peptide that is fused to the recombinant protein of interest. Because of its hydrophilic nature, the FLAG peptide is likely to be located on the surface of the fusion protein. As a result, the FLAG peptide is easily accessible for cleavage by enterokinase (Ek) and for detection with antibodies. In addition, because of the small size of the FLAG peptide tag, it is not likely to obscure other epitopes, domains, or alter function, secretion, or transport of the fusion protein. The 3xFLAG system is an improvement upon the original system by fusing 3 tandem FLAG epitopes (22 amino acids). Detection of fusion proteins containing 3xFLAG is enhanced up to 200 times more than any other system. Like the original FLAG tag, 3xFLAG is hydrophilic, contains an Ek cleavage site, and is relatively small. Therefore, the risk of altering protein function, blocking other epitopes or decreasing solubility is minimized. 

3xFLAG System Expression Vectors for Ultra-Sensitive

重組蛋白的檢測
The 3xFLAG system is an improvement upon the original system by fusing 3 tandem FLAG epitopes for a total of 22 amino acids. Detection of fusion proteins containing 3xFLAG is enhanced up to 200 times more than any other system. Like the original FLAG tag, 3xFLAG is hydrophilic, contains an Enterokinase cleavage site, and is relatively small. Therefore, the risk of altering protein function, blocking other epitopes or decreasing solubility is minimized. In cases of low-level expression, 3xFLAG is ideal. Our selection of CMV vectors provides options for transient or stable expression of 3xFLAG fusion proteins.
 
Ultrasensitive System - Detect < 10 femtomoles using ANTI-FLAG Antibodies; Ideal for cases of low-level expression in mammalian cells.
Superior Detection - 20-200x more sensitive than any other system.
Versatile - Enhanced detection for immunoprecipitation, Western blots and immunocytochemistry.
Wide Selection of Detection and Purification Products - ANTI-FLAG antibodies, resins, and affinity capture plates.

Figure 1. 3xFLAG Sequence. Removal of N-terminal 3xFLAG tags is possible using enterokinase, which cleaves following the Asp-Asp-Asp-Asp-Lys amino acid sequence at the c-terminal end of the tag.
Figure 2. Western Blot of Original FLAG Versus 3xFLAG. Western blot of purified 3xFLAG-BAP (bacterial alkaline phosphatase) and FLAG-BAP transferred onto a nitrocellulose membrane. Detection was performed with ANTI-FLAG M2 monoclonal primary antibody, anti-mouse-HRP secondary antibody, and ECL chemiluminescent substrate.
Figure 3. Comparative Sensitivity of 3xFLAG. Each protein fusion tag was cloned separately on the C terminal of GST. The purified proteins were diluted from 1 ug to 0.01 ng and analyzed. The limit of detection of each tag was determined by Western blot analysis using the recommended dilutions of each respective primary antibody and secondary anti-mouse IgG-HRP conjugate. The blot was developed using ECL.

CMV啟動子：
Our mammalian expression vectors contain the strong CMV promoter for high-level constitutive expression in mammalian cells. 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. 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.