The nucleotide excision repair (NER) system is conserved from yeast to humans and removes bulky adducts from DNA. Interestingly, NER occurs more rapidly in active genes and in the transcribed strand of these genes. 

This sub-pathway of NER, transcription-coupled nucleotide excision DNA repair (TC-NER), depends on actively transcribing polymerase and specific TC-NER factors: Mfd in E.coli, and the DNA dependent ATPases of the Swif2/Snf2 family Rad26 (yeast) and CSB (human). Human cells containing mutations in the Cockayne syndrome B (CSB) gene show a defect in TC-NER but not in global genome repair. 

Interestingly, E. coli analog Mfd functions as an ATP-dependent DNA translocase that can move stalled RNA polymerase forward on the DNA. In addition, Mfd can displace RNA polymerase from the DNA if an obstacle is found downstream of the polymerase. 

The DNA dependent ATPase activity of Rad26/CSB and the fact that purified CSB binds to RNAPII raises the possibility that these proteins may promote passage of RNAPII through diverse transcriptional blockages as Mfd does in E. coli.

However, the exact molecular mechanism of TC-NER remains widely unknown as well as the biochemical activity of CSB/Rad26. Therefore, we intend to characterize the ATPase activity of Rad26 and link this function to the TC-NER mechanism.