Availability of dihydrofolate reductase affinity handle in expressing human prolactin as a soluble fusion protein.

Human prolactin (PRL) cDNA was successfully expressed in Escherichia coli cells with the aid of a dihydrofolate reductase (DHFR) affinity handle. The formed DHFR-PRL fusion protein was accumulated in E. coli cells as a soluble protein with DHFR activity at 30 degrees C. The fusion protein was highly purified with monitored the DHFR activity by methotrexate-bound affinity chromatography, suggesting the usefulness of the handle even in expressing a large polypeptide as a fusion protein.