Structure of single-stranded virus RNA in situ. II. Optical activity of five tobacco mosaic-like viruses and their components.

ORD and CD spectra of some TM-like viruses and their coat proteins were measured to study a possible role of tryptophan residues in RNA-protein interactions in these viruses. Five viruses of this group, differing in tryptophan content of their coat proteins, were used: v-TM virus (3 tryptophan residues per protein subunit), strains HR and U2 (2 tryptophan residues per subunit), dolihos enation mosaic virus and cucumber virus 4(1 tryptophan residue per subunit). The viruses differ significantly in their ORD and CD spectra and some correlation between these spectra and tryptophan content of coat proteins seems to exist. But an analysis of "intravirus RNA" CD spectra, obtained by subtraction of CD spectra of virus -like protein assemblies from the spectra of intact viruses, shows that the observed differences in optical activity can hardly be explained by tryptophan participation in RNA-protein interactions. The presence of the "additional" peak at 293 nm in the ORD of TM virus had been considered as evidence of tryptophan-RNA interactions in this virus. In the present work such a peak at 293 nm was observed in the ORD of all the 5 viruses studied, irrespective of the tryptophan content in their coat proteins. Besides, we managed to obtain the virus-like protein assemblies preparations which also showed a peak at 293 nm. All these data show that, in all probability, the 293 nm peak in the ORD of TM virus does not result from tryptophan-RNA interactions. It is believed that the difference in the optical activity of RNA particles of TM-like viruses do originate from the differences in the RNA-protein interactions in these viruses, but these interactions can hardly involve tryptophan residues of virus coat proteins.