Cellular COPII proteins are involved in production of the vesicles that form the poliovirus replication complex

Poliovirus (PV) replicates its genome in association with membranous vesicl es in the cytoplasm of infected cells. To elucidate the origin and mode of formation of PV vesicles, immunofluorescence labeling with antibodies again st the viral vesicle marker proteins 2B and 2BC, as well as cellular marker s of the endoplasmic reticulum (ER), anterograde transport vesicles, and th e Golgi complex, was performed in BT7-H cells. Optical sections obtained by confocal laser scanning microscopy were subjected to a deconvolution proce ss to enhance resolution and signal-to-noise ratio and to allow for a three -dimensional representation of labeled membrane structures. The mode of for mation of the PV vesicles was, on morphological grounds, similar to the for mation of anterograde membrane traffic vesicles in uninfected cells. ER-res ident membrane markers were excluded from both types of vesicles, and the C OPII components Sec13 and Sec31 were both found to be colocalized on the ve sicular surface, indicating the presence of a functional COPII coat. PV ves icle formation during early time points of infection did not involve the Go lgi complex. The expression of PV protein 2BC or the entire P2 and P3 genom ic region led to the production of vesicles carrying a COPII coat and showi ng the same mode of formation as vesicles produced after PV infection. Thes e results indicate that PV vesicles are formed at the ER by the cellular CO PII budding mechanism and thus are homologous to the vesicles of the antero grade membrane transport pathway.