β Sheets in proteins contain 2 to as many as 22 polypeptide strands, with an average of 6 strands. 

Each strand may contain up to 15 residues, the average being 6 residues.

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.

TLS Online TPP Program

#Id: 6140

#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.

TLS Online TPP Program

#Id: 6141

#Unit 3. Fundamental Processes

TLS Online TPP Program

#Id: 6142

#Unit 3. Fundamental Processes

transcription-coupled repair (TC-NER) TFIIH, itself a large complex, which includes the products of two XP genes, XPB and XPD.