Ultraviolet Photoinactivation Studies on Hybrid Viruses Obtained by the Cross‐reconstitution of the Protein and Rna Components of U(1) and U(2) Strains of Tmv*

The sensitivities of U(1) and U(2) TMV strains to inactivation by ultraviolet light at 253.7 nm were compared with those of hybrid viruses obtained by reconstituting the protein of either native strain with the RNA of the other. In each case, the hybrid virus was found to be virtually identical in sensitivity to the native strain which supplied the protein coat, indicating that the relative sensitivities of the two native strains to ultraviolet light are solely a function of their respective protein coats. Amino acid analysis of the U (2) protein reveals about thirteen or fourteen amino acid replacements compared with the U (1) strain, which is in agreement with earlier studies indicating that there are considerable differences in the protein subunits of the two proteins. Some of the ways in which the observed differences in proteins of the two strains may determine their respective ultraviolet sensitivities are discussed.