A common method for transformation of DNA plasmids into E. coli is the use of chemically competent cells. Although competent cells can be prepared in the laboratory, greater efficiency, reproducibility, and convenience are achieved using Novagen® prepared competent cells. Novagen® Singles™ Competent Cells are designed for ultimate convenience and reliability in plasmid transformation.

• Hosts carry a chromosomal copy of the T7 RNA polymerase gene
• Strains are suitable for production of protein from target genes
• Target genes are cloned in T7 expression vectors, using IPTG as an inducer
• Guaranteed efficiency: >2×10⁶ cfu/µg

Rosetta™ 2 host strains are BL21 derivatives designed to enhance the expression of eukaryotic proteins that contain codons rarely used in E. coli. These strains supply tRNAs for 7 rare codones (AGA, AGG, AUA, CUA, GGA, CCC, and CGG) on a compatible chloramphenicol-resistant plasmid. The tRNA genes are driven by their native promoters.

DE3 indicates that the host is a lysogen of λDE3, and therefore carries a chromosomal copy of the T7 RNA polymerase gene under control of the lac UV5 promoter. Such strains are suitable for production of protein from target genes cloned in pET vectors by induction with IPTG. T7 expression strains are lysogens of bacteriophage DE3, as indicated by the (DE3).