The Stable Association of Virion with the Triple-gene-block Protein 3-based Complex of Bamboo mosaic virus

The triple-gene-block protein 3 (tgbp3) of bamboo mosaic virus (bamv) is an integral endoplasmic reticulum (er) membrane protein which is assumed to form a membrane complex to deliver the virus intracellularly. however,the virus entity that is delivered to plasmodesmata (pd) and its association with tgbp3-based complexes are not known. results from chemical extraction and partial proteolysis of tgbp3 in membrane vesicles revealed that tgbp3 has a right-side-out membrane topology; i.e.,tgbp3 has its c-terminal tail exposed to the outer surface of er. analyses of the tgbp3-specific immunoprecipitate of sarkosyl-extracted tgbp3-based complex revealed that tgbp1,tgbp2,tgbp3,capsid protein (cp),replicase and viral rna are potential constituents of virus movement complex. substantial co-fractionation of tgbp2,tgbp3 and cp,but not tgbp1,in the early eluted gel filtration fractions in which virions were detected after tgbp3-specific immunoprecipitation suggested that the tgbp2- and tgbp3-based complex is able to stably associate with the virion. this notion was confirmed by immunogold-labeling transmission electron microscopy (tem) of the purified virions. in addition,mutational and confocal microscopy analyses revealed that tgbp3 plays a key role in virus cell-to-cell movement by enhancing the tgbp2- and tgbp3-dependent pd localization of tgbp1. taken together,our results suggested that the cell-to-cell movement of potexvirus requires stable association of the virion cargo with the tgbp2- and tgbp3-based membrane complex and recruitment of tgbp1 to the pd by this complex. © 2013 chou et al.