Biomaterial Database

Site-specific frame-shift mutagenesis by the 1-nitropyrene-DNA adduct N-(deoxyguanosin-8-y1)-1-aminopyrene located in the (CG)3 sequence: effects of SOS, proofreading, and mismatch repair. 1996

S A Malia, and R R Vyas, and A K Basu

Department of Chemistry, University of Connecticut, Storrs 06269, USA.

1-Nitropyrene (1-NP), the predominant nitropolycyclic hydrocarbon found in diesel exhaust, is a mutagen and tumorigen. Nitroreduction is a major pathway by which 1-NP is metabolized. Reductively activated 1-NP forms a major DNA adduct, N-(deoxyguanosin-8-yl)-1-aminopyrene (dGAP), both in vitro and in vivo. In Salmonella typhimurium 1-NP induces a CpG deletion in a CGCGCGCG sequence. In Escherichia coli, however, mostly -1 and +1 frame-shifts are observed, which occur predominantly in 5'-CG, 5'-GC, and 5'-GG sequences. In order to determine the mechanism of mutagenesis by dGAP in a CpG repetitive sequence, we constructed a single-stranded M13 genome containing the adduct at the underscored deoxyguanosine of an inserted CGCGCG sequence. In E. coli strains with normal repair capability the adduct induced approximately 2% CpG deletions, which was 20-fold that of the control. With SOS, the frequency of frame-shift mutations increased to 2.6%, even though the frequency of CpG deletion accompanied 50% reduction. The enhancement in mutagenesis was due to a +1 frame-shift that occurred at a high frequency. In strains with a defect in methyl-directed mismatch repair, 50-70% increase in mutation frequency was observed. When these strains were SOS induced, frame-shift mutagenesis increased by approximately 100%. When transfections were carried out in dnaQ strains that are impaired in 3'-->5'exonuclease activity of DNA polymerase III, frame-shift mutagenesis increased 5-7-fold. dGAP-induced frame-shifts in the (CG)3 sequence, therefore, varied from 2% to 17% depending on the state of repair of the host cells. We conclude that dGAP induces both -2 and +1 frame-shifts in a CpG repetitive sequence and that these two mutagenic events are competing pathways. The CpG deletion does not require SOS functions, whereas the +1 frame-shifts are SOS-dependent. On the basis of the data in repair-deficient strains, it appears that both types of frame-shifts occurred as a result of misalignment, which are corrected primarily by the proofreading exonuclease of the DNA polymerase. Misaligned structures that escape the exonuclease are repaired by the methyl-directed mismatch repair, albeit with limited efficiency.

UI	MeSH Term	Description	Entries
D008957	Models, Genetic	Theoretical representations that simulate the behavior or activity of genetic processes or phenomena. They include the use of mathematical equations, computers, and other electronic equipment.	Genetic Models,Genetic Model,Model, Genetic
D008969	Molecular Sequence Data	Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.	Sequence Data, Molecular,Molecular Sequencing Data,Data, Molecular Sequence,Data, Molecular Sequencing,Sequencing Data, Molecular
D009153	Mutagens	Chemical agents that increase the rate of genetic mutation by interfering with the function of nucleic acids. A clastogen is a specific mutagen that causes breaks in chromosomes.	Clastogen,Clastogens,Genotoxin,Genotoxins,Mutagen
D011721	Pyrenes	A group of condensed ring hydrocarbons.
D003849	Deoxyguanosine	A nucleoside consisting of the base guanine and the sugar deoxyribose.
D004260	DNA Repair	The removal of DNA LESIONS and/or restoration of intact DNA strands without BASE PAIR MISMATCHES, intrastrand or interstrand crosslinks, or discontinuities in the DNA sugar-phosphate backbones.	DNA Damage Response
D004269	DNA, Bacterial	Deoxyribonucleic acid that makes up the genetic material of bacteria.	Bacterial DNA
D004926	Escherichia coli	A species of gram-negative, facultatively anaerobic, rod-shaped bacteria (GRAM-NEGATIVE FACULTATIVELY ANAEROBIC RODS) commonly found in the lower part of the intestine of warm-blooded animals. It is usually nonpathogenic, but some strains are known to produce DIARRHEA and pyogenic infections. Pathogenic strains (virotypes) are classified by their specific pathogenic mechanisms such as toxins (ENTEROTOXIGENIC ESCHERICHIA COLI), etc.	Alkalescens-Dispar Group,Bacillus coli,Bacterium coli,Bacterium coli commune,Diffusely Adherent Escherichia coli,E coli,EAggEC,Enteroaggregative Escherichia coli,Enterococcus coli,Diffusely Adherent E. coli,Enteroaggregative E. coli,Enteroinvasive E. coli,Enteroinvasive Escherichia coli
D001483	Base Sequence	The sequence of PURINES and PYRIMIDINES in nucleic acids and polynucleotides. It is also called nucleotide sequence.	DNA Sequence,Nucleotide Sequence,RNA Sequence,DNA Sequences,Base Sequences,Nucleotide Sequences,RNA Sequences,Sequence, Base,Sequence, DNA,Sequence, Nucleotide,Sequence, RNA,Sequences, Base,Sequences, DNA,Sequences, Nucleotide,Sequences, RNA
D012329	RNA, Bacterial	Ribonucleic acid in bacteria having regulatory and catalytic roles as well as involvement in protein synthesis.	Bacterial RNA