Effect of thymine glycol on transcription elongation by T7 RNA polymerase and mammalian RNA polymerase II

Thymine glycols are formed in DNA by exposure to ionizing radiation or oxid ative stress. Although these lesions are repaired by the base excision repa ir pathway, they have been shown also to be subject to transcription-couple d repair. A current model for transcription-coupled repair proposes that RN A polymerase II arrested at a DNA lesion provides a signal for recruitment of the repair enzymes to the lesion site. Here we report the effect of thym ine glycol on transcription elongation by T7 RNA polymerase and RNA polymer ase II from rat liver. DNA substrates containing a single thymine glycol lo cated either in the transcribed or nontranscribed strand were used to carry out in vitro transcription. We found that thymine glycol in the transcribe d strand blocked transcription elongation by T7 RNA polymerise similar to 5 0% of the time but did not block RNA polymerise It. Thymine glycol in the n ontranscribed strand did not affect transcription by either polymerase. The se results suggest that arrest of RNA polymerase elongation by thymine glyc ol is not necessary for transcription-coupled repair of this lesion. Additi onal factors that recognize and bind thymine glycol in DNA may be required to ensure RNA polymerise arrest and the initiation of transcription-coupled repair in vivo.