Processing of placental peptide hormones synthesized in lysates containing membranes derived from tunicamycin-treated ascites tumor cells.

To examine the relationship between pre-protein cleavage and nascent chain glycosylation placental mRNA was translated in a reconstituted ascites cell-free system containing microsomal membranes prepared from tunicamycin-treated or untreated ascites tumor cells. In the absence of membranes, first trimester RNA directed the synthesis of the pre-form of the alpha subunit of human chorionic gonadotropin, whereas, in the presence of normal membranes, first trimester RNA directed the synthesis of a glycosylated form of the alpha subunit. Cell-free lysates containing membranes derived from tunicamycin-treated cells synthesized an alpha subunit protein with little, if any, carbohydrate. This protein was apparently sequestered into membranes since it was resistant to the action of trypsin which was added after translation. The pre-peptide of the alpha subunit protein was removed by treated membranes as determined by amino acid sequence analyses. The non-glycosylated protein pre-placental lactogen was also cleaved to its mature form by tunicamycin membranes. These data strongly suggest that, in vitro, glycosylation is not obligatory for pre-protein cleavage and sequestration of these placental protein hormones.