A KINETIC ISOTOPE EFFECT IN THE PHOTOREACTIVATION OF U.V.‐INACTIVATED TOBACCO MOSAIC VIRUS RNA *

Abstract— Inactivation of tobacco mosaic virus RNA (TMV‐RNA) by u.v. radiation is slower in D2O than in H2O, and TMV‐RNA which has been inactivated in D2O is photoreactivated faster (on Pinto bean) than TMV‐RNA which has been inactivated in H2O. The maximum amount of photoreactivation is unaffected by the solvent, H2O or D2O, present during irradiation. These deuterium isotope effects for inactivation and photoreactivation suggest that pyrimidine hydrates are photoreactivable lesions on Pinto bean.