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Proteins which bind to the DNA damaged by genotoxic agents can be detected in all living organisms. Damage-recognition proteins are thought to be generally involved in DNA repair mechanisms. On the other hand, the relevance to DNA repair of some other proteins which show elevated affinity to damaged DNA (e.g. HMG-box containing proteins or histone H1) has not been established. Using the electrophoretic mobility-shift assay we have investigated damage-recognition proteins in nuclei from rat hepatocytes. We detected two different protein complexes which preferentially bound the DNA damaged by N-acetoxy-acetylaminofluorene. One of them also recognized the DNA damaged by benzo(a)pyrene diol epoxide (yet with much lower efficiency). The proteins which bind to damaged DNA are permanently present in rat cells and their level does not change after treatment of animals with the carcinogens. Differences in the affinity of the detected damage-recognition proteins to DNA lesion evoked by either carcinogen did not correlate with more efficient removal from hepatic DNA of 2-acetylaminofluorene-induced adducts than benzo(a)pyrene-induced ones.
Proteins recognizing DNA damaged by the chemical carcinogen N- acetoxy-acetylaminofluorene (AAAF) were analyzed in nuclear extracts from rat tissues, using a 36 bp oligonucleotide as the substrate and an electrophoretic mobility shift assay. Two major proteins that form complexes with DNA damaged by AAAF were detected; one of them also bound DNA damaged by cis-diammine-dichloroplatinum. The complex specific for AAAF-damaged DNA contained protein loosely attached to nuclear components. It was extracted with 0.1 M NaCl. The amount of this protein was estimated at about 105 copies per liver cell nucleus, and its probable size was about 42 kDa as detected by the Southwestern blotting assay. Its affinity for DNA damaged by AAAF was ~10-fold higher than that for undamaged DNA. Analogous AAAF- DDB (damaged-DNA-binding) proteins were also detected in extracts from rat brain, testis and kidney tissue. The levels of such proteins were not affected in rats treated with the carcinogen 2-acetylaminofluorene.
Proteins recognizing DNA damaged by the chemical carcinogen N-acetoxy-acetylaminofluorene (AAAF) were analyzed in nuclear extracts from rat tissues, using a 36 bp oligonucleotide as a substrate and electrophoretic mobility shift and Southwestern blot assays. One major damage-recognizing protein was detected, whose amount was estimated as at least 105 copies per cell. Levels of this protein were similar in extracts from brain, kidney and liver, but much lower in extracts from testis. The affinity of the detected protein for DNA damaged by AAAF was about 70-fold higher than for undamaged DNA. DNA damaged by cis-diamminedichloroplatinum (cis-DDP), benzo(a)pyrene diolepoxide (BPDE) or UV-radiation also bound this protein with an increased affinity, the former more strongly and the latter two more weakly as compared to AAAF-damaged DNA. The detected AAAF/DDP-damaged-DNA-binding (AAAF/DDP-DDB) protein had a molecular mass of about 25 kDa and was distinct from histone H1 or HMGB proteins, which are known to have a high affinity for cis-DDP-damaged DNA. The level of this damage-recognizing protein was not affected in rats treated with the carcinogen 2-acetylaminofluorene. The activity of an AAAF/DDP-DDB protein could also be detected in extracts from mouse liver cells but not from the Hep2G human hepatocellular carcinoma.
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