The p115-interactive proteins GM130 and giantin participate in endoplasmicreticulum-Golgi traffic

The transport factor p115 is essential for endoplasmic reticulum (ER) to Go lgi traffic. P115 interacts with two Golgi proteins, GM130 and giantin, sug gesting that they might also participate in ER-Golgi traffic. Here, we show that peptides containing the GM130 or the giantin p115 binding domain and anti-GM130 and anti-giantin antibodies inhibit transport of vesicular stoma titis virus (VSV)-G protein to a mannosidase II-containing Golgi compartmen t, To determine whether p115, GM130, and giantin act together or sequential ly during transport, we compared kinetics of traffic inhibition, Anti-p115, anti-GM130, and anti-giantin antibodies inhibited transport at temporally distinct steps, with the p115-requiring step before the GM130-requiring sta ge, and both preceding the giantin-requiring stage. Examination of the dist ribution of the arrested VSV-G protein showed that anti-p115 antibodies inh ibited transport at the level of vesicular-tubular clusters, whereas anti-G M130 and anti-giantin antibodies inhibited after the VSV-G protein moved to the Golgi complex. Our results provide the first evidence that GM130 and g iantin are required for the delivery of a cargo protein to the mannosidase II-containing Golgi compartment, These data are most consistent with a mode l where transport from the ER to the cis/medial-Golgi compartments requires the action of p115, GM130, and giantin in a sequential rather than coordin ate mechanism.