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

Mutagenesis of Golgi resident membrane proteins (glycosyltransferases and coronavirus M protein) revealed an involvement of the transmembrane domain and/or the exoplasmic flanking sequence in retention (Nilsson et al., 1991; Munro, 1991; Aoki et al., 1992; Burke et al., 1992; Colley et al., 1992; Russo et al., 1992; Tang et al., 1992; Teasdale et al., 1992; Wong et al., 1992; Dahdal and Colley, 1993; Machamer et al., 1993; Ponnambalam et al., 1994) . Two models for Golgi retention mechanisms have been proposed. According to the "kin recognition" hypothesis homodimeric proteins may form large hetero-oligomers with other residents of the same Golgi compartment by interaction via their transmembrane and/ or stalk regions. The size of these kin oligomers would prevent their inclusion into transport vesicles. The retained mutants of H1 might participate in trans-Golgi hetero-oligomers by an interaction that is stericaUy hindered by larger cytoplasmic domains.