SUMMARY

Circular dichroism studies (CD) of turnip yellow mosaic virus (TYMV) nucleo-protein and of its isolated RNA and capsid revealed that: (i) the nucleic acid structure, which comprises a considerable amount of base pairing and/or stacking, remains essentially unchanged irrespective of whether the RNA is encapsidated or free; (ii) the secondary structure of the protein component is mainly accounted for by fl-and irregular forms without appreciable amounts &a-helix; (iii)the inter-action of capsid protein and RNA induces some conformational changes in the protein probably involving a decrease of fl-structure and a perturbation of the microenvironment of some aromatic residues. The influence of temperature on the CD spectra of virus nucleoprotein, RNA and capsid was also investigated. The results are discussed in connection with particle stability