A new UV-sensitive mutant that suggests a second excision repair pathway in Neurospora crassa.
In an attempt to understand the relationship between photorepair and dark repair in Neurospora crassa, a new mutant was isolated, which showed defects in both repair processes. The new mutant, mus-38, is moderately sensitive to UV and shows imperfect photoreactivation following UV irradiation. DNA was purified from this mutant and the other UV-sensitive mutants, and analyzed for the removal of cyclobutane pyrimidine dimers (CPDs). UV-specific endonuclease-sensitive sites (ESS) completely disappeared with 1 h of photoreactivation in mus-38 DNA, although the survival recovery with photoreactivation was greatly reduced in this mutant. This suggests that the insufficient survival recovery with photoreactivation in mus-38 does not result from a failure of photo-reversal of CPDs. Removal of ESS during liquid holding (dark repair) was slower in mus-38 compared to wild type. To test the possibility that this mutant was involved in excision repair, the double mutant was made between mus-38 and mus-18, which encodes a UV-damage-specific endonuclease. CPD excision in the mus-18 null mutant was severely affected but not completely inhibited. The double mutant showed a complete loss of the excision activity and was super sensitive to UV. These results indicate that mus-38 participates in an excision pathway that is different from the mus-18 pathway. The mus-38 mutant was sensitive not only to UV but also to some chemical mutagens which make adducts on DNA. Thus, mus-38 is possibly involved in an excision-repair pathway that is related to the Saccharomyces cerevisiae RAD3 pathway.
Ishii
C
C
Department of Regulation Biology, Faculty of Science, Saitama University, Urawa, Japan. chizu@seitai.saitama-u.ac.jp
Nakamura
K
K
Inoue
H
H
D004260:DNA Repair / Q000235:genetics*; D004271:DNA, Fungal / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D003624:Darkness; D003850:Deoxyribonuclease I / Q000378:metabolism; D016296:Mutagenesis; D009153:Mutagens / Q000633:toxicity; D009154:Mutation; D009492:Neurospora crassa / Q000235:genetics* / Q000302:isolation & purification; D011740:Pyrimidine Dimers; D014466:Ultraviolet Rays
D004271:DNA, Fungal; D009153:Mutagens; D011740:Pyrimidine Dimers; D003850:Deoxyribonuclease I