A Golgi retention signal in a membrane-spanning domain of coronavirus E1 protein

We attempted to define the sequence requirements for retention of El . The amino acid sequence of ml is not unusual for a membrane-spanning domain (Fig. 4 B) . When comparing the sequences of four El proteins from different coronaviruses however (18), we noticed that the polar uncharged residues spaced throughout the ml domain were conserved (Fig. 5 A) . These polar residues line up on one side of a predicted alpha helix when the sequence is modeled . We asked if three of these polar residues (Asn22, Thr33, and Gln37) were required for proper targeting of El by changing them individually or in combination to hydrophobic isoleucines. In addition, we inserted two isoleucines in the middle ofml to disrupt the potential amphipathicity ofthe helix. We also changed one of the conserved hydrophobic residues The Journal of Cell Biology, Volume 115, 1991 (Leu30) to a polar Gln (see Fig. 5 A for a summary of mutations) . The mutations were introduced into both the wildtype El protein and the mutant protein Om2,3, which has only the first of the three membrane-spanning domains and is reta6ied in the Golgi region like the wild-type protein.