Targeting of protein ERGIC-53 to the ER/ERGIC/cis-Golgi recycling pathway

The mannose-specific lectin ERGIC-53 (Schindler et al., zer et al., 1988 (Schindler et al., zer et al., , 1990 (Schindler et al., zer et al., , 1991 . Due to continuous recycling, ERGIC-53 and its rat homologue p58 (Saraste and Svensson, 1991) are also present at lower concentrations in the rough ER and in the first fenestrated cis-cisternae of the stacked Golgi (Foguet, M., and H.-P. Hauri, unpublished observation; Schweizer et al., 1988; Chavrier et al., 1990) . ERGIC-53 is a 53-kD nonglycosylated type I transmembrane protein that assembles into equal amounts of disulfide-linked homodimers and homohexamers (Schweizer et al., 1988; Schindler et al., 1993) . It has a large lumenal domain exhibiting homology to leguminous lectins and mammalian galectins, a single transmembrane segment, and a short 12-amino acid long cytoplasmic domain (Schindler et al., 1993; Fiedler and Simons, 1994; Arar et al., 1995) . The cytoplasmic domain contains a COOH-terminal tetrapeptide, KKFF, matching the consensus for a di-lysine ER-retrieval signal.