Family members include TGBp3 proteins found in many plant viruses. Triple gene block 3 proteins (TGBp3) are involved in virus momvement. TGBp3 is an integral ER membrane protein with a single transmembrane domain, and a C-terminal region exposed to the cytosol. TGBp3 is able to target TGBp2 to the cortical ER tubules of the cell periphery through the sorting signal in the C-terminal region of TGBp3. Moreover, it plays a key role in virus cell-to-cell movement by enhancing the TGBp2- and TGBp3-dependent plasmodesmata (PD) localization of TGBp1; however, the enhancement is abolished when one of the two conserved Cys residues in the C-terminal region of TGBp3 is replaced with Ala [1].

1: The cysteine residues at the C-terminal tail of Bamboo mosaic virus triple gene block protein 2 are critical for efficient plasmodesmata localization of protein 1 in the same block. Ho TL, Lee HC, Chou YL, Tseng YH, Huang WC, Wung CH, Lin NS, Hsu YH, Chang BY; Virology. 2017;501:47-53. PMID:27863274