^{Escherichia coli strain BL21 is one of the widely used bacterial hosts for high-level recombinant protein production and for other applications. Here, we present the complete genome sequence of a commercial version of the Escherichia coli BL21 strain.} Here, we describe how the protein expression of human gene fragments in E. coli strains BL21(DE3) and Rosetta(DE3) was evaluated in two stages. Initially a test set of 68 recombinant proteins that previously had been expressed in BL21(DE3) was retransformed and expressed in Rosetta(DE3). High-Control(tm) BL21(DE3) (Lucigen) F - ompT gal dcm hsdS B (r B-m B-) (DE3)/Mini-F lacI q1 (Gent r) The HI-Control BL21(DE3) cells contain a single-copy BAC plasmid harboring a specially engineered version of the lacI q1 repressor allele. The lacI q1 allele expresses ~170-fold more lac repressor protein than the wild-type lacI gene.

A one-way ANOVA with Dunnett's multiple comparison test was employed to evaluate differences in expression levels of recombinant protein between Evo21(DE3) and other expression hosts. P values

^{We utilized the expression of the N-terminal His-tagged kinases in BL21 (DE3) E. coli strain for baseline comparison with four different expression improvement techniques: the addition of external folding chaperones and using the specialized strains: Rosetta, BL21 (DE3) pLysS, and Arctic Express.} .