The gene for insulin-like growth factor I (IGF-I) was constructed from chemically synthesized deoxyoligonucleotides and expressed in Escherichia coli, under the control of a trp promoter, as a set of fusion proteins which were connected with a portion of human growth hormone through the recognition sequence for a sequence-specific protease, either blood coagulation factor Xa or alpha-thrombin. Upon induction with 3-indoleacrylic acid, fusion proteins accumulated with a yield of 10-30% of the total protein. A fusion protein connected through a tetradecapeptide (Asp-Asp-Pro-Pro-Thr-Val-Glu-Leu-Gln-Gly-Leu-Val-Pro-Arg) was efficiently and correctly cleaved by alpha-thrombin, and the purified IGF-I possessed somatomedin-like activity, as determined by the enhancement of sulfation of glycosaminoglycans in cultured costal chondrocytes from rabbits.
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Nishikawa et al. (1987) studied this question.