Requirements for the high-level expression of murine interleukin-3 cDNA inEscherichia coli

Abstract

Murine interleukin-3 (Mu IL-3) cDNA was previously expressed inEscherichia coli using atac promoter and a constitutive high copy number plasmid vector. We found that significant increases in expression levels could be realized by using thetac promoter for the expression of Mu IL-3 in a plasmid vector possessing a temperature-inducible runaway-replicon. In contrast, use of anlpp promoter under similar conditions did not result in an increase in the Mu IL-3 expression level. Significant differences were observed when the expression levels of IL-3 were monitored in variousE. coli hosts having different genetic backgrounds. A mutant ofE. coli which lacks the protease La was found to increase the level of IL-3 produced. This report describes the effect of a specific protease-deficientE. coli host strain, as well as the effect of different promoters and plasmid replicons on the expression levels and stability of a heterologous gene product.