Noncanonical Role for the Host Vps4 AAA+ ATPase ESCRT Protein in the Formation of Tomato Bushy Stunt Virus Replicase
Figure 10
A model on the role of Vps4p during TBSV replication in wild type yeast and the replication defect in vps4Δ yeast.
(A) The formation of tombusvirus-induced spherules (membrane invaginations) in the peroxisomal membranes is facilitated by the recruitment of the shown ESCRT proteins by the monoubiquitinated p33 replication protein. While the ESCRT-III components are likely recruited to the sites of replication to facilitate VRC assembly, the role of ESCRT-II factors, if any, are currently unknown. The TBSV replication model predicts that the scission of the membranous neck and the removal of the ESCRT-III proteins (Vps20p, Vps2p, Vps24p and Snf7p) by Vps4p AAA+ ATPase might be blocked by interaction with the p33 replication protein. Altogether, Vps4p becomes a permanent component of the spherule-like structure. Vps4p might also be involved in the release of the newly-made TBSV (+)RNA (not shown). (B) In the absence of Vps4p, the ESCRT-III proteins do not work properly and tombusvirus replication proteins could only form membrane invaginations with large openings that make the viral replicase complex RNase-sensitive.