[The cloning, expression, purification and bioactivity identification of recombinant IGF-I]

The fragment containing IGF-I cDNA and cyc1 terminator from PSK-IGF-I plasmid was cloned into PSK43 SB treated by Hind III, Klenow and Cla I, generating a recombinant PSB-IGF-I (DH), which have double Hind III sites. This plasmid was treated by Hind III and Klenow, ligated to give a recombinant plasmid PSB-IGF-I(NH), which has no Hind III site. After analysed by restriction endonucleases and sequencing, the fusion site was verified to be correct. This plasmid was excised and a BamH I-Cla I fragment containing yeast alpha-factor promotor, leader sequence, IGF-I cDNA and cycl terminator was cloned into yeast episomal plasmid vector YEpHC8, generating a recombinant plasmid YEpHC8-IGF-I. Transformed this plasmid into yeast competence cells BJ1990 by using LiAc method. The expressed products were secrected into the medium broth and having the correct molecular weight of 8,100 on SDS-PAGE. The products of IGF-I were raised by using high-cell-density fermentation of Saccharomyces cerevisiae. The cleared supernatant of yeast medium was applied to Bio-Rex 70 resin, eluted with 1 mol/L ammonium acetate, pH8.0. Main peak was pooled and applied to Bio-Gel P10 (200-400 mesh). The second peak was collected and get relatively pure IGF-I proteins. The biological activities of IGF I product was assayed in NIH3T3 cells by using MTT method. The results show that the expressed IGF-I can obviously stimulate NIH3T3 cells to proliferate at the concentration ranging from 10 ng/ml to 50 ng/ml, suggesting that the protein has its biological activities.