Bacterial Expression

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For bacterial expression of recombinant proteins, your goal is 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.

Engineered Strains for Optimized Bacterial Protein Expression

Merck’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.

	Transformation Efficiency	Reaction Size	Application
GigaSingles™	>1.0 x 109 cfu/µg	50 µL	High-efficiency cloning
Singles™	>1.5 x 108 cfu/µg	50 µL	Routine cloning
Veggie Singles™	>1.5 x 108 cfu/µg	50 µL	Applications requiring non-animal-derived materials Routine cloning
HT96™	>1.0 x 108 cfu/µg	96 x 20 µL	High-throughput cloning
Standard	>1.5 x 108 cfu/µg	20 µL	Routine cloning

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) Singles™ Competent Cells (Catalog No. 70235)

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.

• BL21(DE3)pLysS Singles™ Competent Cells(Catalog No. 70236)
• Veggie BL21(DE3)pLysS Singles™ Competent Cells (Catalog No. 71253)

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.

• Origami™ 2(DE3) Singles Competent Cells (Catalog No. 71408)

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.

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• Rosetta™ 2(DE3) Singles Competent Cells (Catalog No. 71400)
• Rosetta™ 2 (DE3) pLysS Singles Competent Cells (Catalog No. 71401)

Overnight Express Protocol

The Overnight Express™ Autoinduction Systems enable regulated protein expression in E. coli, without monitoring the culture or adding inducer during cell growth. The simplified protocol offers great convenience, allowing you to focus on your research while it does its job. Learn more about our overnight express protocol.