Abstract
The nucleic acids of 3 strains of tobacco mosaic virus were digested with pancreatic ribonuclease and the resulting products were separated into 20 fractions by a two-dimensional mapping procedure employing paper electro-phoresis and paper chromatography. Maps of the 3 strains were qualitatively very similar. Quantitative analysis of the various fractions showed no significant differences between strains M and TMV, but revealed several striking differences between the strain HR and the other 2 strains. The differences brought out by the mapping procedure are considered to reflect altered patterns of nucleotide sequence in the original polynucleotide chains.