title: Formation and repair of O6-methylguanine in recombination hot spots of plant chromosomes.
abstract: Mutagen-induced chromatid aberrations are not randomly distributed along the metaphase chromosomes. In the field bean (Vicia faba), defined late-replicating and transcriptionally inactive heterochromatic regions are preferentially involved. After exposure to the alkylating agent N-methyl-N-nitrosourea (MNU) (10(-3) M, 1 hour), 70% of all aberrations are clustered within 6 segments containing tandemly repeated FokI elements of 59 bp, which comprise approximately 10% of the genome. Using immuno-slot-blot analyses, we have studied the frequency of O6-methylguanine (O6-MeG), a mutagenic lesion important for aberration induction, in total genomic DNA as well as in FokI sequences of the field bean after exposure to MNU. In either case, similar numbers of adducts per nucleotide were found immediately after treatment as well as after 18 hours of recovery, when most adducts were removed and significant amounts of chromatid aberrations were detectable. Peculiarities of long FokI element arrays (e.g., formation of specific tertiary structures), resulting in error-prone recombination repair, rather than preferential formation or delayed repair of O6-MeG are apparently responsible for aberration clustering in these hot spot regions.
authors.affiliation: Institut für Pflanzengenetik und Kulturpflanzenforschung, Gatersleben, Germany.
authors.forename: P
authors.initials: P
authors.lastname: Baranczewski
authors.forename: P
authors.initials: P
authors.lastname: Nehls
authors.forename: R
authors.initials: R
authors.lastname: Rieger
authors.forename: U
authors.initials: U
authors.lastname: Pich
authors.forename: M F
authors.initials: MF
authors.lastname: Rajewsky
authors.forename: I
authors.initials: I
authors.lastname: Schubert
mesh_terms: D000477:Alkylating Agents / Q000633:toxicity; D002842:Chromatids / Q000187:drug effects; D002869:Chromosome Aberrations; D002875:Chromosomes / Q000187:drug effects*; D004260:DNA Repair; D018744:DNA, Plant / Q000187:drug effects; D015252:Deoxyribonucleases, Type II Site-Specific / Q000187:drug effects / Q000235:genetics*; D007887:Fabaceae / Q000187:drug effects / Q000235:genetics*; D006147:Guanine / Q000031:analogs & derivatives* / Q000032:analysis / Q000378:metabolism; D015151:Immunoblotting; D018519:Meristem / Q000187:drug effects / Q000235:genetics; D008770:Methylnitrosourea / Q000633:toxicity; D009153:Mutagens / Q000633:toxicity; D018517:Plant Roots / Q000187:drug effects / Q000235:genetics; D010946:Plants, Medicinal; D011995:Recombination, Genetic; D012091:Repetitive Sequences, Nucleic Acid
chemical_list: D000477:Alkylating Agents; D018744:DNA, Plant; D009153:Mutagens; D006147:Guanine; D008770:Methylnitrosourea; C008449:O-(6)-methylguanine; C035042:endodeoxyribonuclease FokI; D015252:Deoxyribonucleases, Type II Site-Specific