Degradation of RNA of partially uncoated tobacco mosaic virus during extraction from tobacco leaves

Extracts of tobacco leaves, 3 to 22 hr after infection with 32P‐labeled tobacco mosaic virus (TMV), were analysed by sucrose density‐gradient centrifugation. As reported previously, a shoulder appeared on the lighter side of the main peak representing intact parent viruses. The shoulder was shown to contain partially uncoated virus particles with sedimentation constants of about 140–150 S, which withstood dialysis against a phosphate buffer. RNA from the uncoated particles was isolated on the sucrose density‐gradient, and its sedimentation constant was estimated at 16–18 S. Intact TMV‐RNA and RNA having 16–18 S were also obtained directly from homogenates of tobacco leaves infected with 32P‐TMV. 32P‐TMV was partially stripped by SDS and was added to tobacco leaf sap to test the RNase activity in tobacco leaves. A part of RNA which was exposed by SDS was digested and the 32P‐radioactivity in the top zone of the centrifugation tube increased. This finding supported the idea that the partially uncoated virus particles in infected leaves lost a portion of their RNA during extraction by the action of the RNase contained in the homogenate.

Effects of formycin B on tobacco mosaic virus multiplication

Formycin B (FMB), when applied for 5–6 hr immediately after inoculation, inhibited tobacco mosaic virus (TMV) multiplication in tobacco leaf‐discs and local lesion formation on bean leaves. The inhibitory activity of FMB on local lesion formation was reversed by the addition of adenine, adenosine, and adenylic acid of 5 times in molar concentration as much as FMB, but not by hypoxanthine or uracil. FMB‐treatment did not cause significant changes in total RNA contents and in the synthetic rates in TMV‐inoculated and noninoculated tobacco leaf‐discs. However, 32P incorporation rates into TMV and the amount of TMV synthesized in leaf‐discs were remarkably reduced by FMB‐treatment. 32P‐phosphorylated FMB could not be detected either from FMB‐treated tobacco leaf RNA or from TMV‐RNA by means of column chromatography. 3H‐labeled FMB could not be detected in either TMV or in tobacco leaf RNA. The inhibitory action of FMB against TMV multiplication in tobacco leaf‐discs is discussed.

The structure of tobacco mosaic virus from base analogue treated tobacco leaves

Structure of TMV containing the base analogues such as 2‐thiouracil, 8‐azaguanine, and 5‐fluorouracil was studied. TMV containing these analogues had the same anion‐exchange chromatographic properties as had normal TMV, and 2‐thiouracil was incorporated into TMV particles, probably into TMV‐RNA. Cation‐exchange chromatographic properties of TMV containing these analogues had no significant difference as compared with those of normal TMV. TMV containing 2‐thiouracil was more stable to alkali degradation than normal TMV. Alkali‐degraded TMV containing 2‐thiouracil and normal TMV was characterized by chromatography. These results suggest that not surface structure but internal structure of TMV containing 2‐thiouracil was different from that of normal TMV.