a. In addition to its role in NER, the XPG protein appears to play a role in transcription-coupled BER.
b. Cells with XPG/CS mutations but not with XPG/NER mutations are defective in transcription-coupled BER of thymine glycols.
a. The UvrA protein binds, as a dimer, to a single molecule of the UvrB protein. The resulting complex binds to DNA and preferentially localizes to damaged regions, whereupon the UvrA protein dissociates, leaving UvrB stably bound to the damaged region.
b. The XPA protein is also involved in recognizing and binding to damaged DNA. In addition, it interacts with RPA, TFIIH and ERCC1.
c. The molecular function of CSA is not yet clear, but it's essential for transcription-coupled NER and BER, and it interacts in vitro with the p44 subunit of TFIIH and with CSB.
d. RPA interacts with XPA to enhance its affinity for damaged regions in DNA, and it interacts with XPG. As a single-stranded DNA binding protein, RPA undoubtedly binds to and stabilizes the single-stranded regions that are intermediates in NER.
In this diagram of thymine glycol, the R represents H in true thymine glycol, and it represents a bond to the 1' carbon of 2'-deoxyribose in thymidine glycol or in DNA. Thymine glycols in DNA are repaired by BER.