Endoplasmic reticulum degradation of a subunit of the asialoglycoprotein receptor in vitro. Vesicular transport from endoplasmic reticulum is unnecessary.

The H2a subunit of the human asialoglycoprotein receptor is rapidly degraded from the endoplasmic reticulum (ER) when expressed in CHO15B cells. We have reconstituted ER degradation of H2a in semipermeable cells. At least the initial step in degradation (a proteolytic cleavage inhibited by N alpha-p-tosyl-L-lysine chloromethyl ketone and L-1-tosylamido-2-phenylethyl chloromethyl ketone) can occur in vitro in the presence of guanosine 5'-3-O-(thio)triphosphate or in the absence of ATP and postnuclear supernatant, conditions that do not allow vesicular transport of subunit H1 from the ER to the Golgi. We conclude that vesicular transport from the ER is not required for ER degradation of H2a to occur and thus that it takes place in the ER itself.