Expression of recombinant human growth hormone in a soluble form in Escherichia coli by slowing down the protein synthesis rate

Formation of inclusion bodies is usually observed when foreign proteins are overexpressed in E. coli. The formation of inclusion bodies might be prevented by lowering the rate of protein synthesis, and appropriate regulation of the protein expression rate may lead to the soluble expression. In this study, human growth hormone (rhGH) was expressed in a soluble form by slowing down the protein synthesis rate, which was controlled in the transcriptional and translational levels. The transcriptional level was controlled by the regulation of the amount of RNA polymerase specific to the promoter in front of the rhGH gene. For lowering the rate of translation, the T7 transcription terminator-deleted vector was used to synthesize the longer mRNA of the target gene because the longer mRNA is expected to reduce the availability of free ribosomes. In both methods, the percentage of soluble expression increased when the expression rate slowed down, and more than 93% of rhGH expressed was a soluble form in the T7 transcription terminator-deleted expression system.