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DNA repair defect in xeroderma pigmentosum group C and complementing factor from HeLa cells
M K Shivji1, A P Eker, R D Wood
1Imperial Cancer Research Fund, Clare Hall Laboratories, South Mimms, Herts, United Kingdom.
The Journal of Biological Chemistry
|September 9, 1994
Summary
Researchers purified a key protein that complements DNA repair defects in xeroderma pigmentosum group C (XP-C) cells. This XP-C complementing factor is crucial for early DNA repair stages, aiding in incision formation for genetic damage.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Xeroderma pigmentosum group C (XP-C) is a major inherited syndrome.
- XP-C cells exhibit deficient DNA nucleotide excision repair in bulk DNA but can repair transcribed strands of active genes.
Purpose of the Study:
- To purify and characterize the factor that complements the DNA repair deficiency in XP-C cells.
- To elucidate the role of the XP-C complementing factor in DNA repair pathways.
Main Methods:
- Purification of the XP-C complementing factor from HeLa cells.
- Microinjection of the factor into XP-C fibroblasts to assess in vivo activity.
- Hydrodynamic measurements for molecular mass determination.
- DNA-binding assays using single-stranded DNA cellulose.
Main Results:
- A 160 kDa factor was purified that complements XP-C cell extracts and increases unscheduled DNA synthesis in XP-C fibroblasts.
- The factor binds tightly to single-stranded DNA cellulose.
- The XP-C factor is required early in the repair process, before gap-filling synthesis.
- XP-C cell extracts showed some unstable incision activity on UV-irradiated DNA.
Conclusions:
- The XP-C complementing factor plays a role in forming one of the incisions flanking DNA damage during nucleotide excision repair.
- In transcribed DNA, this function may be carried out by RNA polymerase and/or transcription coupling factors.
- The factor's role is not primarily in chromatin processing for enzyme access.