The dose-response curves for the synthesis of rRNA and avian sarcoma virus mRNA, after irradiation of virus-infected chicken embryo fibrolast cells, have shoulders (P. B. Hackett, H. E. Varmus, and J. M. Bishop, 1981. Virology, 112, 714-728). We tested the hypothesis that the shoulders were the result of dark repair of transcription-terminating lesions after irradiation by measuring the amounts of rRNA synthesized at various times after the uv dose was applied. Our data support the hypothesis and indicated that the rate of repair in transcribed genes of chicken cells is about one or two lesions removed per 106 base pairs of DNA per minute during the first 3 hr after irradiation.
Bibliographical noteFunding Information:
the American Cancer Society Grant, VC-70. P.B.H. was supported by fellowships from the Damon Runyon-Walter Winchell Cancer Fund and a National Service Research Award from the National Institutes of Health.