The synthesis of human placental lactogen by ribosomes derived from human placenta

In a very active cell free system containing polysomes derived from human placenta and a cell sap fraction prepared from ascites tumor cells, the synthesis of the hormone human placental lactogen (HPL) was detected. The identification was based on the following: The in vitro synthesized protein labeled with [³⁵S]methionine migrated at the same rate as authentic HPL on sodium dodecyl sulfate polyacrylamide gels; and tryptic fingerprint analysis of the labeled protein yielded peptides having the same mobilities as seen with the same analysis of purified HPL. The amount of HPL synthesized in a cell free system containing polysomes derived from term placenta was about 10% of the total proteins synthesized and in a comparable system containing first trimester ribosomes the level of synthesis was about 5%. These data suggest the potential for quantitating the HPL messenger RNA (mRNA) activity as a function of the period of gestation and for isolating the mRNA itself.