The translation of a human placental lactogen mRNA fraction in heterologous cell-free systems: The synthesis of a possible precursor

RNA extracted from term placental homogenates directed the synthesis of human placental lactogen (HPL) in a heterologous cell-free system derived from Krebs II ascites tumor cells. HPL was one of the major products synthesized. It was identified on SDS-polyacrylamide gels and by trypsin fingerprinting. Translation of placental RNA in a cell-free system from wheat germ resulted in the synthesis of a protein that migrated slower than HPL on SDS-polyacrylamide gels; no labeled protein was observed that comigrated with authentic HPL. This heavier protein had a molecular weight of about 25,000. It contained the same overlapping HPL tryptic peptides seen when the RNA was translated in the ascites cell-free system. This raises the possibility that a HPL precursor was synthesized in the wheat germ system.