title: Uncoupling of the recBC ATPase from DNase by DNA crosslinked with psoralen.
abstract: Exonucleolytic cleavage of DNA by the recBC DNase is accompained by a DNA-dependent ATP hydrolysis that ceases when the DNA that has been digested to a limit. On the other hand, DNA that has been crosslinked by 4,5',8-trimethylpsoralen in the presence of 360-nm light remains an effective cofactor in the ATPase reaction, but is resistant to digestion by the enzyme. Psoralentreated DNA is degraded by pancreatic DNase, micrococcal nuclease, and Escherichia coli B restriction enzyme, but not by Neurospora crassa nuclease, suggesting that crosslinking did not grossly distort the duplex structure of the DNA. The psoralen-DNA is not a potent inhibitor, but competes with single-stranded DNA from bacteriophage fd for the recBC DNase to roughly the same extent as does normal duplex DNA. DNA treated with psoralen in the dark, exposed to 360-nm light in the absence of psoralen, or treated with the intercalating agents ethidium bromide, 9-aminoacridine, ICR-191, or actinomycin D, responds to the enzyme no differently from untreated DNA. However, DNA crosslinked with mitomycin C or nitrogen mustard behaves similarly to psoralen-treated DNA. The relationship of these findings to models for the function and control of the recBC ATPase and nuclease, and the advantages of psoralen as a DNA crosslinking agent, are discussed.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D002247:Carbon Isotopes; D002499:Centrifugation, Density Gradient; D003090:Coliphages / Q000378:metabolism; D003374:Coumarins / Q000494:pharmacology*; D004269:DNA, Bacterial / Q000378:metabolism*; D004277:DNA, Single-Stranded / Q000378:metabolism; D004279:DNA, Viral / Q000378:metabolism / Q000528:radiation effects; D003609:Dactinomycin / Q000494:pharmacology; D003851:Deoxyribonucleases / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology; D004996:Ethidium / Q000494:pharmacology; D005663:Furans / Q000494:pharmacology; D008040:Genetic Linkage; D008836:Micrococcal Nuclease / Q000378:metabolism; D009492:Neurospora crassa / Q000201:enzymology; D010179:Pancreas / Q000201:enzymology; D011485:Protein Binding; D011830:Radiation Effects; D011995:Recombination, Genetic; D014316:Tritium; D014466:Ultraviolet Rays
chemical_list: D002247:Carbon Isotopes; D003374:Coumarins; D004269:DNA, Bacterial; D004277:DNA, Single-Stranded; D004279:DNA, Viral; D005663:Furans; D014316:Tritium; D003609:Dactinomycin; D003851:Deoxyribonucleases; D008836:Micrococcal Nuclease; D000251:Adenosine Triphosphatases; D004996:Ethidium