Skip to main content
. 2012 May 24;8(5):e1002726. doi: 10.1371/journal.ppat.1002726

Figure 8. A proposed model illustrating the differential involvement of NbHsp90 in BaMV and satBaMV RNA replication.

Figure 8

The scenario with BaMV genomic RNA is shown on the left and satBaMV RNA on the right. The 3′ UTR regions are enlarged to depict various structural domains as indicated by capital letters A through E. NbHsp90 is represented by the long oval with N-terminal (N), middle (M), and C-terminal (C) domains shown. Following infection and uncoating, ORF1-encoded protein (Rep) is translated using BaMV genomic RNA as the template. Initially, the newly translated Rep is not properly folded, as represented by the irregular string of grey circles. NbHsp90 is thought to be involved in both the proper folding of BaMV Rep and the recruitment of BaMV RNA template in the early stage of replication. Firstly, Hsp90 inhibitors GA or 17-AAG can inhibit NbHsp90, whose chaperone activity assists in the proper folding of Rep (represented by light grey ovals) and in the assembly of active replicase complexes with other host factors. Once the active replicase complexes are assembled, the GA or 17-AAG inhibitory effects (represented by the T-shaped line) are alleviated. Secondly, the NbHsp90 RNA-binding domain (M-domain), which is insensitive to inhibition by GA or 17-AAG, interacts specifically with domain E of BaMV 3′ UTR and recruits templates into the active replicase complexes. Alternatively, NbHsp90 may bind to BaMV 3′ UTR first and facilitate both the proper folding of Rep as it is newly translated and the assembly of a replication initiation complex on the BaMV 3′ UTR. By contrast, the satBaMV RNA 3′ UTR may have evolved efficient structures that serve as a scaffold for the proper folding of Rep in the absence of domain E, and facilitates the assembly of active replicase complexes with other host factors (indicated by the dashed line labeled “2”). Additionally, satBaMV RNA may utilize the preformed replicase complexes on BaMV genomic RNA for their own replication (indicated by the dashed line labeled “1”). Thus, replication of satBaMV RNA is independent of NbHsp90, and hence is insensitive to the inhibitory effects of GA and 17-AAG.