Xeroderma pigmentosum complementation group C cells remove pyrimidine dimers selectively from the transcribed strand of active genes.
We have measured the removal of UV-induced pyrimidine dimers from DNA fragments of the adenosine deaminase (ADA) and dihydrofolate reductase (DHFR) genes in primary normal human and xeroderma pigmentosum complementation group C (XP-C) cells. Using strand-specific probes, we show that in normal cells, preferential repair of the 5' part of the ADA gene is due to the rapid and efficient repair of the transcribed strand. Within 8 h after irradiation with UV at 10 J m-2, 70% of the pyrimidine dimers in this strand are removed. The nontranscribed strand is repaired at a much slower rate, with 30% dimers removed after 8 h. Repair of the transcribed strand in XP-C cells occurs at a rate indistinguishable from that in normal cells, but the nontranscribed strand is not repaired significantly in these cells. Similar results were obtained for the DHFR gene. In the 3' part of the ADA gene, however, both normal and XP-C cells perform fast and efficient repair of either strand, which is likely to be caused by the presence of transcription units on both strands. The factor defective in XP-C cells is apparently involved in the processing of DNA damage in inactive parts of the genome, including nontranscribed strands of active genes. These findings have important implications for the understanding of the mechanism of UV-induced excision repair and mutagenesis in mammalian cells.
Venema
J
J
MGC-Department of Radiation Genetics and Chemical Mutagenesis, State University of Leiden, The Netherlands.
van Hoffen
A
A
Karcagi
V
V
Natarajan
A T
AT
van Zeeland
A A
AA
Mullenders
L H
LH
D000243:Adenosine Deaminase / Q000235:genetics*; D001483:Base Sequence; D002460:Cell Line; D004247:DNA / Q000235:genetics / Q000528:radiation effects*; D004251:DNA Transposable Elements; D005347:Fibroblasts / Q000502:physiology / Q000528:radiation effects; D005796:Genes / Q000528:radiation effects*; D005816:Genetic Complementation Test; D006801:Humans; D008969:Molecular Sequence Data; D011740:Pyrimidine Dimers; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics*; D014158:Transcription, Genetic; D014466:Ultraviolet Rays; D014983:Xeroderma Pigmentosum / Q000235:genetics*
D004251:DNA Transposable Elements; D011740:Pyrimidine Dimers; D004247:DNA; D013762:Tetrahydrofolate Dehydrogenase; D000243:Adenosine Deaminase