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ompT, hsdSB(rB-rB-), dcm, gal
The strain contains DE3, a λ prophage carrying the T7 RNA polymerase gene under control of the lac UV5 promoter and lacIq. IPTG is required to induce expression of the T7 RNA polymerase. Protein expression from transforming plasmids containing a T7 promoter-driven expression system is repressed until IPTG induction of T7 RNA polymerase expression occurs. The strain does not contain the lon protease and is also deficient in the outer membrane protease, OmpT. The lack of two key proteases reduces the degradation of heterologous proteins expressed in the strain. The helper plasmid pLysS constitutively expresses low levels of T7 lysozyme, which reduces basal level expression of recombinant genes by inhibiting basal levels of T7 RNA polymerase. pLysS also carries the chloramphenicol resistance gene and the p15A origin for compatibility with plasmids containing the ColE1 or pMB1 origin.
Studier and Moffatt, J. Mol. Biol. 189 (1986), 113-130 PMID: 3537305