Blockage of RNA polymerase II at a cyclobutane pyrimidine dimer and 6-4 photoproduct.

The blockage of transcription elongation by RNA polymerase II (pol II) at a DNA damage site on the transcribed strand triggers a transcription-coupled DNA repair (TCR), which rapidly removes DNA damage on the transcribed strand of the expressed gene and allows the resumption of transcription. To analyze the effect of UV-induced DNA damage on transcription elongation, an in vitro transcription elongation system using pol II and oligo(dC)-tailed templates containing a cyclobutane pyrimidine dimer (CPD) or 6-4 photoproduct (6-4PP) at a specific site was employed. The results showed that pol II incorporated nucleotides opposite the CPD and 6-4PP and then stalled. Pol II formed a stable ternary complex consisting of pol II, the DNA damage template, and the nascent transcript. Furthermore, atomic force microscopy imaging revealed that pol II stalled at the damaged region. These findings may provide the basis for analysis of the initiation step of TCR.