Bacterial Strain JM109(DE3), derived from JM109, contains a chromosomal copy of the gene for T7 RNA polymerase. JM109(DE3) is used for the high-level expression of genes cloned into vectors for expression of sequence downstream from the T7 promoter, provided that the cloned sequence contains a ribosomal binding site. Please note: JM109(DE3) cannot be used for blue/white selection.