Transcription-coupled repair: a complex affair

Transcription-coupled repair (TCR) is generally observed as more rapid or more efficient removal of certain types of DNA damage from the transcribed strands of expressed genes compared with the nontranscribed strands. It has been clearly demonstrated to be a subpathway of nucleotide excision repair (NER) in E. coli, yeast and mammalian cells. Genetic and biochemical studies indicate that it is a highly complex process and requires the participation of the NER pathway, the RNA polymerase complex and additional factors. An early event in TCR is likely the blocking of RNA polymerase complex elongation by damage present in the transcribed strands of expressed genes. Whether TCR is involved in base excision repair pathways or the repair of common forms of oxidative damage is less clear. This review is focused on the description of possible mechanisms of TCR in E. coli and mammalian cells.