The Golgi sorting domain of coronavirus E1 protein.

The coronavirus E1 membrane protein is confined to the Golgi after it is expressed in cells either by viral infection or via injection of synthetic RNA. We have investigated the features of the protein responsible for intracellular sorting and found that a C-terminal deletion of only 18 amino acids results in its transport to the plasma membrane. However, we have previously shown that this C-terminal region alone is not sufficient for Golgi retention. When E1 was fused to a cell-surface protein, Thy-1, the resulting molecule was retained in the Golgi. Various mutated forms of E1 whose destinations were the ER, cell surface or lysosomes were also fused to Thy-1, and in each case the fusion was sorted according to its E1 component alone. We argue that, in contrast to sorting signals for other membrane compartments, Golgi retention of E1 is not due to a single short peptide sequence. Instead, the Golgi 'signal' of E1 appears to require for its expression a domain comprising most of the sequence of the protein.