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 cellfree 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 α subunit of human chorionic gonadotropin, whereas, in the presence of normal membranes, first trimester RNA directed the synthesis of a glycosylated form of the α subunit. Cell-free lysates containing membranes derived from tunicamycin-treated cells synthesized an α 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 α subunit protein was removed by treated membranes as determined by amino acid sequence analyses. The nonglycosylated 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.