Vesicular stomatitis virus glycoprotein contains a dominant cytoplasmic basolateral sorting signal critically dependent upon a tyrosine

To investigate the contribution of the cytoplasmic domain of the vesicular stomatitis virus G glycoprotein to its basolateral expression in polarized epithelial cells, chimeric proteins containing the external and transmembrane domains of an apically targeted protein, the influenza virus hemagglutinin (HA), and either the G cytoplasmic domain or an unrelated cytoplasmic sequence, were introduced into Madin-Darby canine kidney (MDCK) cells. Addition of the cytoplasmic tail of G to a truncated HA resulted in delivery of greater than 95% of the chimeric protein to the basolateral cell surface, indicating that the G cytoplasmic domain contains a dominant basolateral sorting signal. A similar chimera, containing the cytoplasmic tail of herpes simplex I glycoprotein gC, was not sorted basolaterally. Deletion of the cytoplasmic tail from G protein itself decreased the fidelity of sorting to the basolateral surface, but not the extent to which the protein reached the plasma membrane. Mutation of cytoplasmic tyrosine 501 of G caused an identical loss of basolateral targeting, suggesting that the tyrosine, or the sequence surrounding it, is required for efficient basolateral transport of G. Mutation of tyrosine 501 had no effect on internalization of G, which was much slower than that of endocytic receptors. Thus, VSV G protein contains an efficient cytoplasmic basolateral targeting signal that is not an efficient internalization signal.