CHANGE IN THE BASE COMPOSITION OF MESSENGER RNA OF ESCHERICHIA COLI BY ULTRAVIOLET IRRADIATION AND ITS RECOVERY

Abstract— The base composition of messenger RNA in Escherichia coli B/r and B _8–1 irradiated with ultraviolet (u.v.) light has been examined. The experimental results are as follows: (1) the synthesis of rapidly labeled RNA does not stop in ultraviolet irradiated bacteria. (2) The rapidly labeled RNA in irradiated cells shows a change in base composition corresponding to the formation of pyrimidine dimers in DNA molecules. The mole per cent of adenine component is increased with ultraviolet dose. The ratio of purine/pyrimidine becomes larger and the GC content smaller. (3) The base composition of the rapidly labeled RNA in irradiated bacteria reversed to that in unirradiated cells, when the irradiated cells were reactivated by experimental procedures for photoreactivation or dark reactivation. The reversion in the base composition corresponds well to the decrease in the amount of thymine dimers in DNA molecules. (4) The mechanism of the change in the base composition of rapidly labeled RNA caused by ultraviolet irradiation is discussed.