Intact Genomics (ig®) chemically competent BL21(DE3)pLysS chemically competent cells are suitable for transformation and routine protein expression. The pLysS plasmid produces T7 lysozyme that reduces base-level expression of the gene of interest, subsequently allowing for tighter control of expression and is, therefore, suitable for the expression of toxic genes.  BL21(DE3)pLysS chemically competent cells also carry the chloramphenicol resistance gene.

Transformation efficiency is tested by using the pUC19 control DNA supplied with the kit and using the high efficiency transformation protocol. Transformation efficiency should be greater than 3×10^7 CFU/µg pUC19 DNA. Untransformed cells are tested for appropriate antibiotic sensitivity.