The Over-Expression of Biologically Active Human Growth Hormone in a T5-Based System in Escherichia coli, Studying Temperature Effect

We studied the expression of human growth hormone (hGH) in E. coli under a bacteriophage T5-base promoter in a pQE30 expression vector. For an efficient expression of hGH cDNA, a number of codons at the hGH N-terminal coding region were altered based on the E. coli major codons. An over-expression of hGH in the bacteria, carrying the recombinant plasmids, was observed at 37°C in the presence of IPTG. The over-expression was also observed at 30°C in the absence of IPTG. Therefore a temperature down-shift induction, 37°C to 30°C, was suggested to achieve an over-expression of recombinant hGH (rhGH) without the use of chemical inducers. The pQE30-hGH recombinant plasmids show high stability in the TG1 host in the non-selective conditions. In a batch fermentation condition, the purified rhGH was obtained with the yield of 53 mg/l of culture. We took advantage of the formation of inclusion bodies to recover the rhGH, followed by diafiltration and refolding steps. The purified rhGH was biologically active for its receptor-binding on IM9 cells.