Restoration of potato virus X coat protein capacity for assembly with RNA after His-tag removal.

We found that the fusion of hexahistidine (H)6 tag to the potato virus X (PVX) coat protein (CP) abolished its ability to be assembled with viral RNA into helical nucleoprotein virus-like particles (VLPs). Instead, irregular agglomerates were produced upon incubation of PVX RNA with (H)6-tagged PVX CP. A factor Xa recognition site, IEGR, was inserted upstream of the CP coding sequence. Removal of the (H)6 tag from PVX CP by Xa protease restored its ability to bind RNA and to assemble VLPs. In addition to the canonical IEGR site, the factor Xa protease was found to cleave PVX CP at a second (non-consensus) site, AVTRGR, located close to the C-terminus of PVX CP. The latter cleavage did not affect reassembly of the PVX RNA and CP into VLPs.