Biological significance of domain-oriented DNA repair in xeroderma pigmentosum cells.
The patterns (domain oriented versus a random location) and amounts of DNA excision repair, determined by standard density gradient techniques and sedimentation properties of partially repaired and UV-endonuclease-digested DNA in alkaline sucrose gradients, are reported for UV (254 nm)-irradiated nondividing xeroderma pigmentosum complementation group C or A (XP-C, XP-A) and normal cells. Repair synthesis in relatively UV-resistant XP-C (XP4RO) cells is domain oriented and limited (10% of normal values) while it is randomly located and not as limited in more sensitive XP-A (XP8LO) cells. Thus, greater UV resistance is associated with a very limited but domain-oriented pattern of repair. In XP-C cells, both total and domain-oriented repair syntheses, while limited, increase with UV dose and plateau at about 15-20 J/m2, as observed for normal cells. We suggest that repair in XP-C is limited at the lower UV doses (less than 15-20 J/m2) by substrate levels in specific chromatin domains and not by availability of essential enzymes for domain-oriented repair. In contrast, the XP-A strain XP8LO exhibits normal repair activities for doses up to 5 J/m2 and limited repair at higher doses, indicating that repair occurs through normal pathways that are limited by reduced availability of an essential enzyme.
Kantor
G J
GJ
Department of Biological Sciences, Wright State University, Dayton, Ohio 45435.
Elking
C F
CF
D002460:Cell Line; D002478:Cells, Cultured; D004260:DNA Repair; D004261:DNA Replication / Q000528:radiation effects; D005347:Fibroblasts / Q000378:metabolism / Q000528:radiation effects; D006801:Humans; D007700:Kinetics; D014466:Ultraviolet Rays; D014983:Xeroderma Pigmentosum / Q000378:metabolism*