Expression Technologies Inc.
Many proteins have effects on cellular proliferation and differentiation. As a result, they are toxic to the host cells during heterologous expression. Majority proteins have different degree of toxicity to the host cells. The mechanism of toxicity is different for each protein. We developed special media, vectors, and cell strains to overcome toxicity of recombinant proteins.
The toxicity of recombinant protein results from leaking expression before induction. Over 80% of recombinant proteins expressed in E.coli are induced by IPTG. All of the IPTG-inducible expression systems have leaking expression. These expression systems contain only one lac operator site downstream of 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 minimize leaking expression. These vectors require lacI-over-expressing strains to achieve maximum repression. DetoxTM strains are genetically engineered to over express lacI repressors. DetoxCTM strains are specially designed for cloning and some protein expression. DetoxETM strains are only designed for protein expression using E.coli RNA polymerase. DetoxET7TM will expressed toxic protein with a T7 promoter using T7 RNA polymerase. All toxic proteins tested can be successfully cloned and expressed in our special media, vectors, and cell strains as soluble and functional proteins.
Although our detoxification strains were originally designed for our proprietary vectors, we found these strains are useful in expressing toxic proteins in all IPTG-inducible vectors tested. For example, vector containing toxic protein A cannot be established in any commercially available expression strains such as plysS, plysE, placI, C41 and C43, but it can be established in a DetoxETM strain and expressed at high level (lane 1). Toxic protein B is poorly expressed in a commercial detoxification strain plysS (lane 5), but it is highly expressed in a DetoxETM strain (lane 3). Lanes 2 and 4 are none-induced controls. Please click on each strain name for more information.
All these strains are compatible with expression vectors derived from ColE1 replication origins such as those from pBR322 or pUC plasmids and have a selection marker other than chloramphenicol. Our other detoxification strains will meet your expression needs if your vector contain a chloramphenicol selection marker or a pACYC origin.
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Detoxification cell strains
All of the cell strains with TM superscripts are trademarks of Expression Technologies Inc. They are all patent-pending. These cell strains are for non-commercial research use only they cannot be distributed out of the purchasing lab. Please contact us for any other uses.
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1. Oehler S. et al., (1994) EMBO J. 13, 3348-3355