A specific transmembrane domain of a coronavirus E1 glycoprotein is required for its retention in the Golgi region.

The E1 glycoprotein of the avian coronavirus infectious bronchitis virus contains a short, glycosylated amino-terminal domain, three membrane-spanning domains, and a long carboxy-terminal cytoplasmic domain. We show that E1 expressed from cDNA is targeted to the Golgi region, as it is in infected cells. E1 proteins with precise deletions of the first and second or the second and third membrane-spanning domains were glycosylated, thus suggesting that either the first or third transmembrane domain can function as an internal signal sequence. The mutant protein with only the first transmembrane domain accumulated intracellularly like the wild-type protein, but the mutant protein with only the third transmembrane domain was transported to the cell surface. This result suggests that information specifying accumulation in the Golgi region resides in the first transmembrane domain, and provides the first example of an intracellular membrane protein that is transported to the plasma membrane after deletion of a specific domain.