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

In this paper, we have shown that the first of the three membrane-spanning domains of the model Golgi protein IBV El contains a signal for retention. When the single membrane-spanning domain of a model plasma membrane protein (VSV G) was replaced with the ml sequence from El, the chimeric Gml was retained in the Golgi region of transfected cells . Another plasma membrane protein (am), was also retained in the Golgi region when ml replaced the normal membrane-spanning domain, but not when m3 was inserted . The uncharged polar residues that line one face of the alpha helix predicted for ml seem to be the important feature of this sequence . Changing any of three polar residues to an Ile, or insertion of two Ile residues into the middle of ml in the El protein Om2,3 (with the second and third membrane-spanning domains deleted) resulted in transport to the plasma membrane . Thus, ml was shown to be necessary and sufficient for Golgi retention when it was the only membrane-spanning domain in the protein . With further mutagenesis, we are in the process of determining whether the exact sequence of polar residues is required for Golgi retention, or if the polar nature of one side of the helix is the important feature .