In Vitro Photoreactivation of Ultraviolet‐inactivated Ribonucleic Acid From Tobacco Mosaic Virus

Treatment of ultraviolet‐inactivated tobacco mosaic virus ribonucleic acid (TMV–RNA) with extracts obtained from the local lesion host, Nicotiana tabacum var. Xanthi , n.c., and simultaneous illumination at 365 nm results in up to a four‐fold increase in infectivity over non‐illuminated controls. The active material in the extract appears to be associated with protein, based on its inactivation by boiling, precipitation with ammonium sulfate, and exclusion from Bio‐Rad P100 polyacrylamide. Partially purified DNA photoreactivating enzyme from yeast or pinto bean has no activity on ultraviolet‐irradiated TMV–RNA.