APC/C consists of 14 core subunits in metazoans and 13 core subunits in yeast.

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#Unit 3. Fundamental Processes

XPC= UvrA

XPA and XPD = UvrB, RPA

ERCC1-XPF, XPG = UvrC

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#Unit 3. Fundamental Processes

XPC detect distortions = UvrA in E. coli

Formation of the bubble involves the helicase activities of the proteins XPA and XPD (the equivalent to UvrB in E. coli) and the single-strand-binding protein RPA. The bubble creates cleavage sites 5’ to the lesion for a nuclease known as ERCC1-XPF and 3’ to the lesion for nuclease XPG (representing the function of UvrC). In higher cells, the resulting DNA strand is 24–32 nucleotides long. As in bacteria, the DNA strand is released to create a gap that is filled in by the action of DNA polymerase and ligase.

XPB and XPD are both helicases; the XPB helicase is required for promoter melting during transcription, while the XPD helicase performs the unwinding function in NER

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#Unit 3. Fundamental Processes

XP patients cannot excise pyrimidine dimers and other bulky adducts. Mutations occur in one of eight genes called XPA to XPG

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#Unit 3. Fundamental Processes

XP-V is caused by a defect in the translesion DNA polymerase, Pol n. The gene encoding Pol n is sometimes called XPV

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#Unit 3. Fundamental Processes

In global genome repair (GG-NER), the XPC protein detects the damage and initiates the repair pathway. XPC can recognize damage anywhere in the genome. In mammals, XPC is a component of a lesion-sensing complex that also includes the proteins HR23B and centrin2.

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#Unit 3. Fundamental Processes

UV-induced cyclobutane pyrimidine dimers (CPDs), are not well recognized by XPC. In this case, the DNA damage-binding (DDB) complex assists in recruiting XPC to this type of damage.