Cells of the responding tissue must have both, 

A receptor protein for the inducing factor 

The ability to respond to the signal

TLS Online TPP Program

#Id: 6134

#Unit 3. Fundamental Processes

The modified base can be repaired before replication by DNA glycosylase via the base excision pathway. If replication occurs before the oxoG is removed, resulting in the misincorporation of an A, then a fail-safe glycosylase can remove the A, allowing it to be replaced by aC. This provides a second opportunity for the DNA glycosylase to remove the modified base.

TLS Online TPP Program

#Id: 6135

#Unit 3. Fundamental Processes

XPC= UvrA

XPA and XPD = UvrB, RPA

ERCC1-XPF, XPG = UvrC

TLS Online TPP Program

#Id: 6136

#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

TLS Online TPP Program

#Id: 6137

#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

TLS Online TPP Program

#Id: 6138

#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

TLS Online TPP Program

#Id: 6139

#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.