Automated chemical synthesis of a protein growth factor for hemopoietic cells, interleukin-3.

Interleukin-3 (IL-3), a protein of 140 amino acids, was chemically synthesized by means of an automated peptide synthesizer and was shown to have the biological activities attributed to native IL-3. Assays of synthetic analogues established that an amino terminal fragment has detectable IL-3 activity, but that the stable tertiary structure of the complete molecule was required for full activity. The results demonstrate that automated peptide synthesis can be applied to the study of the structure and function of proteins.