SIMILAR PROCESSES MEDIATE GLYCOPEPTIDE EXPORT FROM THE ENDOPLASMIC-RETICULUM IN MAMMALIAN-CELLS AND SACCHAROMYCES-CEREVISIAE

Glycopeptides are transported from the lumen of the yeast endoplasmic reticulum (ER) to the cytosol and in contrast to secretory proteins do not enter ER-to-Golgi transport vesicles, In a cell-free system, this process is ATP- and cytosol-dependent, While yeast cytosol promotes t he export of glycopeptides fi-om mammalian ER in vitro, glycopeptide r elease cannot be detected in the presence of mammalian cytosol, We dem onstrate that this is due to an N-glycanase activity in mammalian cyto sol rather than lack of glycopeptide transport activity in mammalian m icrosomes. Monitoring the amount of glycopeptide enclosed in ER membra nes we show the cytosol- and ATP-dependent release of glycopeptide fro m mammalian microsomes, The fact that glycopeptide export can be achie ved with ER and cytosol derived from heterologous sources: indicates t hat glycopeptide export from the ER is an important process conserved during evolution.