期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1976
卷号：73
期号：4
页码：1179-1183
DOI：10.1073/pnas.73.4.1179
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Messenger RNA derived from term placenta directs the synthesis of human placental lactogen (hPL, molecular weight 22,200) in an ascites 30,000 X g post-mitochondrial supernate (S-30). When the S-30 is fractionated into ribosome and cell-sap (S-100) fractions, and these are recombined for incubation, term placental mRNA directs the synthesis of a protein with a molecular weight of 25,000. This protein contains authentic hPL tryptic peptides. This suggested that during the separation of ribosomes and S-100 a component responsible for cleavage was lost. A 1.0 M sucrose cushion was used for the preparation of ribosomes and S-100 and membranous material accumulated at the sucrose interphase. When this membrane fraction was added back to the ribosome-S-100 system only hPl was formed. Cleavage was greatest when membranes were added within the first few minutes of incubation. In a run-off system composed of term polysomes, ascites S-100, and the inhibitor of initiation, pactamycin, the 25,000 molecular weight material, referred to as pre-hPL, was also synthesized. These data strongly suggest that (i) pre-hPL is an authentic percursor to hPL, (ii) cleavage of the precursor primarily occurs on nascent, ribosome-bound peptide chains, and (iii) pre-hPL is the primary gene product.
