Biological functions of the cytoplasmic TGBp1 inclusions of bamboo mosaic potexvirus

The TGBp1 protein encoded by the first open reading frame of the triple-gene-block (TGB) of bamboo mosaic potexvirus (BaMV) plays important roles in virus movement; one of them is to shape the viral RNA before its being transported from cell to cell. However, TGBp1 mainly forms cytoplasmic inclusions which are devoid of the RNA-binding activity. With the purified TGBp1 inclusions of BaMV, we analyzed the possibility of dissociation of functional TGBp1 from the inclusions. Our data showed that the cytoplasmic inclusions were able to dissociate continuously functional TGBp1, which possessed ATP-binding, ATPase, and RNA-binding activities. Moreover, the dissociation of TGBp1 was significantly enhanced by the presence of viral RNA and capsid protein (CP), consistent with the finding that TGBp1 are able to form ribonucleoprotein complex with viral RNA and CP. Taken together, these results support the idea that the cytoplasmic TGBp1 inclusions are active pools of TGBp1, upon which viral RNA can be shaped into a transferable form.