trans-Golgi retention of a plasma membrane protein: mutations in the cytoplasmic domain of the asialoglycoprotein receptor subunit H1 result in trans-Golgi retention

Proteins with mutations affecting folding and oligomerization are mostly retained in the ER by chaperones. Mu- tant Hl(A4-33A), however, passes these quality control mechanisms and accumulates in a later compartment of the secretory pathway. The kinetics of ER-to-Golgi transport of Hl(A4-33A), as judged from the conversion of the endo H-sensitive precursor to the endo H-resistant mature form of the protein in pulse-chase experiments, were similar to those of wild-type H1 with 50% conversion after ~3 h (Fig. 7 A) . Cross-linking experiments using difluorodinitrobenzene (Shia and Lodish, 1989) in M1 and M1A cells showed similar formation of homodimers and -trimers of wild-type and mutant H1 (not shown).