THE THERMAL-STABILITY AND DECAPSIDATION MECHANISM OF TYMOVIRUSES - A DIFFERENTIAL CALORIMETRIC STUDY

The thermal stability of virions present in purified suspensions of th ree tymoviruses, turnip yellow mosaic virus (TYMV), belladonna mottle virus (BelMV) and eggplant mosaic virus (EMV) was investigated by micr ocalorimetry. Virions are less stable than natural empty shells at 4.5 less-than-or-equal-to pH less-than-or-equal-to 8.5. Polyvalent cation s present in TYMV stabilize the virions at pH less-than-or equal-to 5. 0 only. Virions decapsidate in three steps: i) the release of the vira l 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 firs t step. Structural implications are discussed.