1. 1. The effects of ultraviolet irradiation of T4 DNA on transcription in vivo and in vitro have been studied and correlated with the inactivation of bacteriophage T4. 2. 2. No reduction in the binding of RNA polymerase to DNA is observed, while the initiation of RNA chains is reduced. 3. 3. The main effect of ultraviolet irradiation of T4 DNA on transcription is the lowering of the rate of RNA synthesis caused by the production of shorter RNA chains. 4. 4. Synthesis of RNA chains is terminated at the site of certain photoproducts on the DNA and not resumed between the photoproduct and the next initiation site. 5. 5. RNA polymerase is released from the irradiated template, but during the transcription cycle the RNA polymerase is associated 1.4 times longer with 1000 erg/mm2 irradiated T4 DNA than with a non-irradiated template. 6. 6. RNA polymerase is inactivated by ultraviolet light to e-1 by 1700 erg/mm2. 7. 7. Chain-terminating photoproducts in the early region of the T4 chromosome account for 40% of the phage-inactivating lesions, and initiation-inhibiting lesions for 2%. 8. 8. We calculate that the early portion of the T4 chromosome consists of 9-10 transcription regions with a number average length of 7000 nucleotide pairs, or 3-4 genes.
Bibliographical noteFunding Information:
This work was supported by National Science Foundation grants GB-8267 (W.S.) and GB-7818 (R.L.M.), and by U.S. Public Health Service training grant No. 5-ToI-GM78I-IO (P.H.B.). We thank the following graduates tudentsa nd technicians for contributingt o this research:A lan R. Br~iutigam,S tephenD. Hughes, John L. McConnell, Thomas D. Stamato, Janet L. Morgan and Carol D. Trotter.