Inactivation of Infectious Nucleic Acid from Tobacco Mosaic Virus by Ultraviolet Light (2537 A)

For an understanding of action spectra in biology it is desirable to investigate the action of ultraviolet light on model substances such as enzymes, viruses, and biologically active nucleic acids (1). Tobacco mosaic virus has been investigated quantitatively by several authors (2-7), and the subject has been reviewed (1, 8). The quantum efficiency for inactivation is very low (5, 6) as compared with typical proteins (1). Considering the size of the virus, however, it is remarkable that the quantum yield is as high as it is (9),2 and it has been suggested that the nucleic acid in the virus may have a greater sensitivity to UV-light than would a biochemically active protein particle of the same size (7). We have determined the sensitivity of inactivation of infectious nucleic acid isolated from TMV and found it to be higher than for the virus itself with the strain tested [Johnson's No. 1 (common TMV) (10)], in accord with the postulate of Bawden and Kleczkowski (7). In addition, we have found that the nucleic acid is inactivated by UV-light without change in viscosity; inactivation is accompanied by a decrease in absorption in the ultraviolet spectrum at 2600 A. The implications of the data are discussed.