Mechanism of ultraviolet-induced mutagenesis: extent and fidelity of in vitro DNA synthesis on irradiated templates. [Escherichia coli]
The effect of uv irradiation on the extent and fidelity of DNA synthesis in vitro was studied by using homopolymers and primed single-stranded phi X174 phage DNA as substrates. Unfractionated and fractionated cell-free extracts from Escherichia coli pol/sup +/ and polA1 mutants as well as purified DNA polymerase I were used as sources of enzymatic activity. (DNA polymerases, as used here, refer to deoxynucleosidetriphosphate : DNA deoxynucleotidyltransferase, EC 2.7.7.7.) The extent of inhibition of DNA synthesis on uv-irradiated phi X174 DNA suggested that pyrimidine dimers act as an absolute block for chain elongation by DNA polymerases I and III. Experiments with an irradiated poly(dC) template failed to detect incorporation of noncomplementary bases due to pyrimidine dimers. A large increase in the turnover of nucleoside triphosphates to free monophosphates during synthesis by DNA polymerase I on irradiated phi X174 DNA has been observed. We propose that this nucleotide turnover is due to idling by DNA polymerase (i.e., incorporation and subsequent excision of nucleotides opposite uv photolesions, by the 3' to 5' ''proofreading'' exonuclease) thus preventing replication past pyrimidine dimers and the potentially mutagenic event that should result.
- Research Organization:
- Univ. Libre de Brussels
- OSTI ID:
- 6589036
- Journal Information:
- Proc. Natl. Acad. Sci. U.S.A.; (United States), Vol. 75:7, Issue 7
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
59 BASIC BIOLOGICAL SCIENCES
DNA
BIOSYNTHESIS
ESCHERICHIA COLI
MUTAGENESIS
RADIOINDUCTION
BACTERIOPHAGES
BIOCHEMICAL REACTION KINETICS
BIOLOGICAL RADIATION EFFECTS
DIMERS
IN VITRO
POLYMERASES
PYRIMIDINES
ULTRAVIOLET RADIATION
AZINES
BACTERIA
BIOLOGICAL EFFECTS
ELECTROMAGNETIC RADIATION
ENZYMES
HETEROCYCLIC COMPOUNDS
KINETICS
MICROORGANISMS
NUCLEIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PARASITES
RADIATION EFFECTS
RADIATIONS
REACTION KINETICS
SYNTHESIS
VIRUSES
560131* - Radiation Effects on Microorganisms- Basic Studies- (-1987)
550200 - Biochemistry