Photohydration of Uridine in the RNA of Coliphage R17, II. The Relationship between Ultraviolet Inactivation and Uridine Photohydration

Uridine photohydrates (6-hydroxy-5,6-dihydrouridine) are the major products formed upon irradiation of the RNA bacteriophage R17 with ultraviolet light at 280 mμ , while cyclobutane-type pyrimidine dimerization does not occur to an appreciable extent. The suppression of dimerization may indicate that the RNA inside the phage is held in a rigid conformation in close contact with the phage protein. A value of 0.94 (± 0.10) uridine photohydrates per biological hit is obtained from a correlation of the fraction of phage surviving with the number of photohydrates formed as a function of ultraviolet dose. It is concluded that uridine photohydrates represent a major part of the lethal damage caused by ultraviolet light in bacteriophage R17. An efficient system for dark repair of uridine photohydration seems to be lacking in E. coli.