Does calcium ion binding control plant virus disassembly

Abstract Hydrogen ion titration data on brome mosaic, turnip crinkle, and turnip yellow mosaic viruses in the presence and absence of calcium ions are presented and analyzed. Published evidence on pH- and divalent ion-dependent changes in other viruses is reviewed in the light of current knowledge about cation-binding sites. It appears that most, perhaps all, plant viruses contain calcium-binding sites with some of the properties to be expected for a switch controlling disassembly. Practical conclusions follow for virus purification and reassembly experiments.