Ultraviolet inactivation and miscoding of irradiated R17-RNA in vitro

Ultraviolet irradiation of the single-stranded Coliphage R17 leads to inactivation of the in vitro messenger activity of its RNA. Uridine-photohydration is the major reaction occurring in the RNA under these conditions. At a residual activity of the synthetase gene of 37 per cent, there are 11.2 uridine-photohydrates present in the total R17 genome, while only 5.3 photohydrates are necessary to decrease the translation of the coat gene to the same value. De novo incorporation of histidine into the coat protein is observed with R17-RNA from ultraviolet-irradiated phage, indicating that uridine-photohydrates can miscode as cytidine in an in vitro translation system.