The transport factor p115 is essential for endoplasmic reticulum (ER) to Golgi traffic. P115 interacts with two Golgi
proteins, GM130 and
giantin, suggesting 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 stomatitis virus (VSV)-
G protein to a
mannosidase II-containing Golgi compartment. To determine whether p115, GM130, and
giantin act together or sequentially 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 stage, and both preceding the
giantin-requiring stage. Examination of the distribution of the arrested VSV-
G protein showed that anti-p115
antibodies inhibited transport at the level of vesicular-tubular clusters, whereas anti-GM130 and anti-
giantin antibodies inhibited after the VSV-
G protein moved to the Golgi complex. Our results provide the first evidence that GM130 and
giantin are required for the delivery of a cargo
protein to the
mannosidase II-containing Golgi compartment. These data are most consistent with a model where transport from the ER to the cis/medial-Golgi compartments requires the action of p115, GM130, and
giantin in a sequential rather than coordinate mechanism.