THE PURINE AND PYRIMIDINE COMPOSITION OF THE TOBACCO MOSAIC VIRUS AND THE HOLMES MASKED STRAIN

Abstract

In recent publications, Markham and Smith (1) and Knight (2) have reported significantly different values for the molar proportions of the purine and pyrimidine bases occurring in tobacco mosaic virus nucleic acid.Slightly different procedures were employed for the preparation of the nucleic acid samples, but the hydrolytic and chromatographic methods used were essentially the same.It seems unlikely that the observed differences were introduced by the procedures used for the isolation of the nucleic acid, because of further results obtained by Knight on nucleic acids prepared from five strains generally considered to be related to tobacco mosaic virus and because of analyses made directly on the intact virus nucleoproteins.When the latter were analyzed directly, the values found for the molar ratios of the bases differed only slightly from the corresponding ones for the isolated nucleic acids and were not considered significantly different.The analyses of the isolated nucleic acids of the six strains gave almost identical results which, within experimental error, were also in agreement with the values for seven other newly derived strains (3).On the basis of these data Knight (2) has suggested that "the nucleic acids of TMV strains may have identical compositions."It is not clear from the abovementioned results whether differences occur in the composition of the tobacco mosaic virus nucleic acid as the virus is produced under differing conditions, or whether the observed differences were due to other unknown factors.Because the strains studied by Knight were produced in Turkish tobacco plants and the common strain in White Burley by Markham and Smith, a possible explanation for the differences found is that the ribonucleic acid composition of the same virus strain may vary, depending on the host species in which the virus is produced.In other publications from this laboratory (4, 5), analytical procedures applicable to the direct analyses of nucleoprotein for their