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.