When expressing recombinant proteins in E. coli, the goals are to obtain high yields of full-length, soluble protein. Whether you are producing protein for enzymatic assays, generating antigen for antibody production, assaying protein-protein interactions, or determining three-dimensional structure – you need high-quality protein, fast. EMD Millipore’s portfolio of bacterial strains for protein expression includes the best all-purpose strains and several specialty strains for difficult-to-express proteins, all backed by unwavering technical support to increase your chances of success. For ultimate convenience and reliability in plasmid transformation, Singles™ Competent Cells are provided in 50 μL volumes to eliminate the need to aliquot, freeze/thaw, or waste partially used vials. This saves time, money, minimizes contamination and ensures reliable cell performance.
BL21(DE3) Singles Competent Cells
BL21 has been the gold standard for protein expression since it was first introduced in 1990. Deficient in Lon and OmpT proteases, BL21 and its derivatives are ideal for many applications. T7 expression strains are lysogens of bacteriophage λDE3, as indicated by the (DE3), and carry a chromosomal copy of the T7 RNA polymerase gene under control of the lacUV5 promoter. Such strains are suitable for production of protein from target genes cloned in appropriate T7 expression vectors.
BL21(DE3)pLysS Singles Competent Cells
The pLysS designation is given to strains carrying a plasmid that encodes T7 lysozyme, a natural inhibitor of T7 RNA polymerase. These strains are used to suppress basal expression of T7 RNA polymerase prior to induction and thus stabilize pET, pCDF, pRSF, pACYCDuet™, pCOLADuet™, and Gateway® Nova pDEST™ recombinants encoding target proteins that affect cell growth and viability.
Origami™ 2(DE3) Singles Competent Cells
Recombinant proteins that depend on disulfide bond formation for proper folding may be difficult to express in bacterial cytoplasm, which is typically a reducing environment. Origami 2 and Origami B strains have mutations in glutathione reductase (gor) and thioredoxin reductase (trxB), facilitating proper disulfide bond formation and increasing yields of folded, soluble protein.
Rosetta™ 2(DE3) Singles Competent Cells
Reduce protein truncation with Rosetta 2 host strains. These strains are BL21 derivatives that enhance the expression of eukaryotic proteins containing codons rarely used in E. coli. These strains supply tRNAs for 7 rare codons (AGA, AGG, AUA, CUA, GGA, CCC, and CGG) on a compatible chloramphenicol-resistant plasmid. The tRNA genes are driven by their native promoters.
HMS174(DE3)pLysS Competent Cells
Are toxic recombinant proteins causing problems with bacterial growth? The HMS174 strain provides high transformation efficiency (>5 x 106 cfu/µg) and the recA mutation in a K-12 background. This mutation may stabilize certain target genes whose products may cause the loss of the DE3 prophage.
