Excision repair of uracil incorporated in DNA as a result of a defect in dUTPase. |
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Authors: | B K Tye I R Lehman |
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Institution: | Department of Biochemistry Stanford University School of Medicine Stanford, Calif. 94305, U.S.A. |
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Abstract: | Mutants of Escherichia coli that are severely defective in the enzyme dUTPase (dut) accumulate short (4 to 5 S) Okazaki fragments following brief pulses with 3H]thymidine. The transient appearance of DNA fragments in these mutants is plausibly explained by the misincorporation of uracil in DNA as a result of an increase in available dUTP, followed by its rapid excision and repair. The evidence in support of this interpretation is the following: (1) accumulation of short DNA fragments can be partially suppressed by a mutation in dCTP deaminase, presumably by decreasing the intracellular level of dUTP relative to dTTP; (2) accumulation of the short DNA fragments can be almost completely suppressed by a mutation in uracil N-glycosidase, probably by preventing the introduction of nicks at the sites of uracil incorporation; (3) introduction of DNA polymerase I or DNA ligase mutations into dUTPase-defective strains results in the persistence of the 4 to 5 S fragments and rapid cessation of DNA synthesis. Uracil N-glycosidase, DNA polymerase I and DNA ligase must therefore be involved in the excision repair of uracil-containing DNA. |
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