[Synthesis of human proinsulin in Escherichia coli cells]

Expression of the synthetic gene for human proinsulin in E. coli has been investigated. The proinsulin gene has been expressed directly under the control of a synthetic promoter of phage fd DNA and a promoter of tryptophan operon, or using fusions with fragments of some bacterial proteins. These fusions gave insoluble polypeptide products amounting to 20-30% of total cellular protein. The scheme for isolating proinsulin from bacterial cells was developed. Proinsulin was cleaved from leader polypeptides by treatment with cyanogen bromide and converted into human insulin.