Expression in Escherichia coli of a chemically synthesized gene for a "mini-C" analog of human proinsulin.

A gene has been constructed which codes for an analog of human proinsulin in which the normal 35-amino acid connecting peptide is replaced by a "mini-C" peptide of six amino acids (Arg-Arg-Gly-Ser-Lys-Arg). The gene, composed of oligonucleotide fragments synthesized by the triester method, was cloned and expressed as a beta-galactosidase hybrid protein. The proinsulin analog was separated from beta-galactosidase by cyanogen bromide cleavage and purified. Controlled disulfide exchange in the S-sulfonate of the analog generated a molecule having high-pressure liquid chromatography (HPLC) and radioimmunoassay (RIA) behavior consistent with a proinsulin-like structure.