Repair of damaged DNA by extracts from a xeroderma pigmentosum complementation group A revertant and expression of a protein absent in its parental cell line

Nucleic Acids Res. 1992 Mar 11;20(5):991-5. doi: 10.1093/nar/20.5.991.


Cells derived from individuals with mutations in the xeroderma pigmentosum complementation group A gene (XP-A gene) are hypersensitive to UV light and have a severe defect in nucleotide excision repair of damaged DNA. UV-resistant revertant cell lines can arise from XP-A cells in culture. Cells of one such revertant, XP129, were previously shown to remove (6-4) photoproducts from irradiated DNA, but to have poor repair of cyclobutane pyrimidine dimers. To analyze the biochemical nature of the reversion, whole cell extracts were prepared from the SV40-immortalized fibroblast cell lines XP12RO (an XP-A cell line), the revertant XP129 (derived from XP12RO), and 1BR.3N (from a normal individual). The ability of extracts to carry out repair synthesis in UV-irradiated DNA was examined, and immunoblots were performed using antiserum that recognizes XP-A protein. XP12RO extracts exhibited a very low level of repair and no detectable XP-A protein, but repair activity could be conferred by adding purified XP-A protein to the reaction mixture. XP129 extracts have essentially normal repair synthesis consistent with the observation that most repair of UV-irradiated DNA by extracts appears to occur at (6-4) photoproducts. An XP-A polypeptide of normal size was present in XP129, but in reduced amounts. The results indicate that in XP129 a mutational event has converted the inactive XP12RO XP-A gene into a form which expresses an active XP-A protein.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Cell Extracts
  • Cell Line
  • DNA Damage / genetics
  • DNA Repair / genetics*
  • DNA-Binding Proteins / genetics*
  • Genetic Complementation Test
  • Humans
  • Immunoblotting
  • Molecular Sequence Data
  • Mutation / genetics
  • Xeroderma Pigmentosum / genetics*
  • Xeroderma Pigmentosum Group A Protein


  • Cell Extracts
  • DNA-Binding Proteins
  • XPA protein, human
  • Xeroderma Pigmentosum Group A Protein