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Plasmid Vectors


Heterologous protein expression becomes increasingly important in the post genomics era. Many proteins have different degree of toxicity to the host cell. The mechanism of toxicity is different for each protein. The toxicity of recombinant protein results from leaking expression before induction. The leaking expression is consequences of insufficient transcription repression  and transcription read-through.

Over 80% of recombinant proteins expressed in E.coli are induced by IPTG. All of the commercial IPTG-inducible expression vectors have leaking expression. These expression vectors contain only one lac operator downstream of an inducible promoter. In natural lac operon, three lac operators control the natural promoter (Reference 1, 2, and 3). Two or three operators are needed for maximum repression (Reference 2). We developed proprietary vectors containing two to three lac operators to maximize transcription repression. In addition, we put a strong terminator immediately before the promoter to stop transcription read-through. All vectors contain lacIq gene which expresses lacI repressor at high level. These vectors require lacI-over-expressing strains to achieve maximum repression. Good repression was also obtained from these vectors in the regular expression strains.

In addition to toxicity, many proteins also have solubility, stability, and functionality problems. Co-expression of these proteins with their molecular chaperones or partners may produce soluble, stable, and functional proteins (Reference 4-10). Our vectors are specially designed for co-expression needs. These vectors contain different selection markers and compatible replication origins. Proteins cloned in our vectors can be individually expressed. They may also be co-expressed within one host cell. Along with our specially engineered cell strains, many proteins have been successfully expressed. For co-expression using our vectors, please click on compatibility.

Our vectors are grouped by antibiotic selection markers they have. We also offer customized DNA constructs (including vectors and plasmids).


Ampicillin vectors provide ampicillin resistance to the host cells. These vectors contain replication origins from pBR322 and pUC19 plasmids.


Chloramphenicol vectors provide chloramphenicol resistance to the host cells. These vectors contain replication origins from pACYC plasmids.


Tetracycline vectors provide tetracycline resistance to the host cells. These vectors contain replication origins from pACYC plasmids.


We also provide customized vectors, plasmids, and any other DNA constructs for both academic and industrial identities. We will make these DNA constructs you specify.


For two plasmid vectors to exist in one cell, they need to have compatible replication origins. In addition, they should have different antibiotic resistance markers to be selected within a cell.


1. Oehler S. et al., (1994) EMBO J. 13, 3348-3355
2. Oehler S. et al., (1990) EMBO J., 9, 973-979
3. Flashner Y. et al., (1988) PNAS, 170, 5588-5593
4. Li C. et al., (1997) PNAS, 94, 2278-2283
5. Shuman S. (1990) J. Biol. Chem. 265, 11960-11966
6. Fribourg S. et al., (2001) J. Mol. Biol. 306, 363-373
7. McNally E. et al., (1988) PNAS 85, 7270-7273
8. Ishiai M. et al., (1996) J. Biol. Chem. 271, 20868-20878
9. Henricksen L et al., (1994) J. Biol. Chem. 269, 11121-11132
10. Stebbins C. et al., (1999) Science 284, 455-461

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