The eukaryotic cell encounters more than one million various kinds of DNA 
lesions per day. The nucleotide excision repair (NER) pathway is one of the most 
important repair mechanisms that removes a wide spectrum of different DNA 
lesions. NER operates through two sub pathways: global genome repair (GGR) and 
transcription-coupled repair (TCR). GGR repairs the DNA damage throughout the 
entire genome and is initiated by the HR23B/XPC complex, while the CSB 
protein-governed TCR process removes DNA lesions from the actively transcribed 
strand. The sequence of events and the role of particular NER proteins are 
currently being extensively discussed. NER proteins also participate in other 
cellular processes like replication, transcription, chromatin maintenance and 
protein turnover. Defects in NER underlay severe genetic disorders: xeroderma 
pigmentosum (XP), Cockayne syndrome (CS) and trichothiodystrophy (TTD).