The incorporation of uracil-2-¹⁴C into nucleic acid, phospholipid and protein fractions of tobacco mosaic virus (TMV)-infected tobacco leaves was investigated. Both inoculated and uninoculated leaf disks were floated on water under continuous illumination of artificial light and they were exposed to ¹⁴C for 1-5 hours at various intervals after inoculation. Then the disks were homogenized with phosphate buffer and fractionated as described in Fig. 1. The specific activity in each fraction was estimated.
The data of Table 1 show that the rate of incorporation of ¹⁴C into nucleic acid fraction, or, to a lesser extent, into phospholipid and protein fractions, of inoculated leaf disks 1 and 3 days after inoculation was significanty greater than that into the corresponding fraction obtained from uninoculated leaf disks. However, at 5 days after inoculation, no significant differences in the rate of incorporation into nucleic acid and phospholipid fractions were found between inoculated and uninoculated leaf disks.
In order to determine the distribution of the incorporated ¹⁴C among the individual bases, nucleic acid fraction was hydrolyzed with 70% HCIO₄ and then chromatographed by the method of Wyatt. Table 3 summarizes the analysis of the ¹⁴C distribution. A large part of ¹⁴C was found in uracil and cytosine, and the specific activity of these bases of inoculated leaf disks 40 hours after inoculation was greater than that of corresponding bases obtained from uninoculated leaf disks.
Using cell-free systems, the incorporation of ¹⁴C into nucleic acid, phospholipid and protein fractions was studied. Tobacco leaf disks were homogenized with phosphate buffer 22 hours after inoculation and ¹⁴C was added to them and the mixture was shaked at 28°C. The data appeared in Tables 5-6. After 2 hours incubation, the rate of incorporation into nucleic acid and phospholipid fractions of inoculated leaf homogenate significantly increased as compared with that of uninoculated leaf homogenate. In this case, the increased amount of radioactivity appeared in nucleic acid fraction was located in both RNA and DNA.
Finally, in order to elucidate the general pattern of incorporation of ¹⁴C into the various cell fractions, the homogenized juice of leaf disks was fractionated as shown in Fig. 2 and the incorporation into nucleic acid of each fraction was determined. The results are summarized in Table 7. The greater part of radioactivity incorporated into the infected and uninfected cell fractions appeared in DNA of Pl fraction, and specific activity of DNA and RNA in Pl fraction of infected cells exceed the comparable value in uninfected cells 2 days after inoculation.

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In this paper experiments are reported concerning the antigenicity and interference with the infectivity of tobacco mosaic virus (TMV) inactivated by ultraviolet radiation (intensity of radiation: 2160μW/cm²) and high temperature treatment. TMV was inactivated by relatively low doses of ultraviolet radiation (30min. at 10cm distance), but showed no remarkable change in antigenic properties, increased irradiation (18 hours at the same distance) being necessary in order to completely destroy its antigenicity. The inactivated TMV interfered with the infectivity of TMV, as demonstrated by comparison of the number of local lesions produced on the leaves of Nicotiana glutinosa inoculated with the mixture of inactivated and active virus solution, with those produced by active virus and buffer solution.
The infectivity of TMV solution decreased by 30 to 70 percent when the inactivated TMV solution of 100 to 10, 000 times its quantity was added to it. Higher concentrations of inactivated TMV results in greater decrease in the infectivity of TMV. Similar interference was recognized in the plants reinoculated with active TMV one day after inoculation of the inactivated TMV, but such was not the case when the active TMV was inoculated more than 3 days later. Antagonistic reactions were found to occur between the active and the inactivated but still antigenic TMV, whereas the completely denatured TMV did not interfere with the former. TMV subjected to high temperature (90° and 95°C., for 10min.) lost both its infectivity and antigenicity, and had no interfering activity. But the TMV incompletely inactivated by heating at 85°C., for 10 minutes showed slight interference with the activity of TMV.

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It has been shown that χ phage attacks almost all motile strains of Salmonella except the serotypes having H antigen g…, l…, or eh and certain strains having 1, 5 or 1, 2. So far, host range mutants of χ had been obtained against each of the resistant strains which have either H antigen l…, eh, or 1, 2, but had not against those having g antigen.
With serial mixed culture method, some new type phages which attack strains having g antigen were isolated. The procedure was to cultivate χ phage together with a χ sensitive, S. abortus-equi SL23, and one of the resistant strains. When the new type phage which can attack the resistant bacteria was not obtained from the mixed culture, the culture was centrifuged and an aliquot of the supernatant was used as the source of χ phage for the second mixed culture. This process was repeated until the new type phage was obtained up to the 10th subculture. Three new type phages were obtained from the serial mixed cultures in which each of NTCT8718, NTCT5723, and SJ26 was chosen as the resistant bacterial strain; they were designated M8, M12, and M26, respectively.
In one step growth of these phages in SL23, the latent period was about 60 minutes as that of the χ phage, and the average burst size was as follows: about 72 in M8, about 301 in M12, about 58 in M26, and about 110 in χ phage. From the K value test, it was showed that χ phage, M8, M12, and M26, were closely related in serological characters. When they were plated with SL23, the difference in plaque morphology could not be detected between χ phage and these new type phages. Similarity in the shape of these phage particles to χ phage was showed by electron microscopy. Host specificity to attack motile bacteria but not nonmotile bacteria was observed on these phages as well as on χ phage. These phages, however, differs from χ phage in their host range. They are able to attack a χ-resistant motile mutant strain, SJ100 derived from S. typhimurium TM2, and several salmonella serotypes having H-antigen g.
Host range mutants which attack SJ100 were isolated easily from χ phage. Among 106 such mutants (hT), two mutants (designated as hT94 and hT97) were able to attack g-group Salmonella as the new type phages described above.
These results strongly suggest that these new type phages derived from χ phage passing through some spontaneous mutational steps; they may be multi-step host range mutants of χ phage. The Salmonella having H-antigen g tested fall into three groups in regard to the responce to the host range mutants: (1) a type which allow the multiplication of phage, (2) a type which is lysed by infection but the lysis is not accompanied with the phage reproduction, and (3) a type which is not lysed. It is likely that the resistance of the Salmonella having H-antigen g to χ phage consists of various numbers of complex factors including the antigenic type determinants.

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