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The Basics• Hereditary, autosomal recessive disorder• Results in a hypersensitivity to UV rays• 1/250,000 have XP in the US
• XP leads to a predisposition to cancer
• Mostly basal and squamous cell carcinomas
• Certain types can lead to neurological disorders
Friedberg, 2001.
What causes XP?• 7 different gene abnormalities identified
that lead to XP
• Complementation groups XPA-XPG
• These genes are crucial for DNA damage repair
Friedberg, 2001.
How genes lead to cancer
UV radiation leads to DNA damage in the form of pyrimidine dimers and photoproducts.
• XP genes respond to damage and carry out NER
• Each complementation group gene has a specific function in NER
Friedberg, 2001.
XPF
• XPF is part of an endonuclease
• Forms a heterodimer complex with ERCC1
• Together, they make 5’ incision ~24 nt away from damage
Friedberg, 2001.
• The damage is transcribed and translated
• If in a gene for controlling cell proliferation then the result is cancer.
• Multiple mutations lead up to cancer.
Xeroderma pigmentosum group F
• Mostly affects Japanese
• Symptoms are milder than in other types of XP, later onset
• Few suffer neurological complications
Identification of XPF
• ERCC4 had been found to correct NER mutations in hamsters.
• It was hybridized to human chromosome and found on #16.
Identification of XPF• Cosmid clones of
chromosome 16 carrying ERCC4 were mapped using fluorescent hybridization.
• It appeared at 16p13.13-p13.2 as predicted
• Linkage to the neo gene present in vector indicated that the human gene was cloned.
Thompson et al, 1994
• S. cerevisiae has a Rad1-Rad10 complex that makes 5’ incision
• Rad10 was known to be the homolog of ERCC1.
• A polypeptide copurified with ERCC1 and thought to be the Rad1 homolog
Identification of XPF
Identification of XPF
• RT-PCR was used with primers created from Rad1• It was used as a probe to find an ORF on C-terminal similar to that of Rad1.• N-terminal of human gene found in database.• Assembled
Sijbers et al, 1996.
• Using in situ hybridization, they found the RAD1 homolog mapped to 16p13.1-13.2
Identification of XPF
Sijbers et al, 1996.
Homolog encodes ERCC4, XPF
• The homolog was transfected into UV sensitive cells
• 3 types: UV41 (ERCC4), UVS1 ERCC11), and 43-3B (ERCC1)
The Results
• Full correction of UV41
• Partial correction of UVS1
• 43-3B cells did not survive
Sijbers et al, 1996.