The thermal stability and decapsidation mechanism of tymoviruses: A differential calorimetric study

The thermal stability of virions present in purified suspensions of three tymoviruses, turnip yellow mosaic virus (TYMV), belladonna mottle virus (VelMV) and eggplant mosaic virus (EMV) was investigated by microcalorimetry. Virions are less stable than natural empty shells at 4.5 ⩽ pH ⩽ 8.5. Polyvalent cations present in TYMV stabilize the virions at pH ⩽ 5.0 only. Virions decapsidate in three steps: i) the release of the viral RNA, probably through a hole in the capsid; ii) the dissociation of the artificial empty shells thus formed; and iii) the denaturation of the dissociated components. An exothermic process accompanies the first step. Structural implications are discussed.