Abstract
Partially purified mRNA coding for the MOPC-315 heavy immunoglobulin alpha chain was translated in a reticulocyte lysate containing 20 labeled amino acids. Radiolabeled MOPC-315 heavy chain precursor protein, purified by preparative gel electrophoresis and immunoprecipitation, was sequenced by Edman degradation. The labeled phenylthiohydantoin amino acid obtained in each cycle was identified and quantitated by high-pressure liquid chromatography. The precursor sequence of 18 amino acids, Met-Lys-Val-Leu-Ser-Leu-Leu-Tyr-Leu-Leu-Thr-Ala-Ile-Pro-His-Ile-Met-Ser, preceded the sequence corresponding to the NH2 terminus of the mature secreted heavy chain.