A circular dichroism study of the Turnip yellow mosaic virus-RNA

We examined the circular dichroism spectra of intact Turnip yellow mosaic virus, freezed/thawed virus, empty capsid particles, and phenol extracted RNA. The circular dichroism signal of the empty capsid was found to contribute for less than 1% to the circular dichroism of the virus. Differences in the circular dichroism spectra indicate that TYMV-RNA exhibits different conformations when it is in situ in the virus, when it has been ejected by freezing/thawing and when it has been phenol extracted. Increase of the ionic strength up to 0.1 M NaCl led to conformational change of the RNA either freezed/thawed ejected or phenol extracted but not in situ in the capsid. Addition of spermidine (3 mM) induced a conformational change only for the phenol extracted RNA. These results are discussed with respect to the origin of the various conformational states of viral RNA.