title: Recombinational and mutagenic repair of psoralen interstrand cross-links in Saccharomyces cerevisiae.
abstract: Psoralen photoreacts with DNA to form interstrand cross-links, which can be repaired by both nonmutagenic nucleotide excision repair and recombinational repair pathways and by mutagenic pathways. In the yeast Saccharomyces cerevisiae, psoralen cross-links are processed by nucleotide excision repair to form double-strand breaks (DSBs). In yeast, DSBs are repaired primarily by homologous recombination, predicting that cross-link and DSB repair should induce similar recombination end points. We compared psoralen cross-link, psoralen monoadduct, and DSB repair using plasmid substrates with site-specific lesions and measured the patterns of gene conversion, crossing over, and targeted mutation. Psoralen cross-links induced both recombination and mutations, whereas DSBs induced only recombination, and monoadducts were neither recombinogenic nor mutagenic. Although the cross-link- and DSB-induced patterns of plasmid integration and gene conversion were similar in most respects, they showed opposite asymmetries in their unidirectional conversion tracts: primarily upstream from the damage site for cross-links but downstream for DSBs. Cross-links induced targeted mutations in 5% of the repaired plasmids; all were base substitutions, primarily T --> C transitions. The major pathway of psoralen cross-link repair in yeast is error-free and involves the formation of DSB intermediates followed by homologous recombination. A fraction of the cross-links enter an error-prone pathway, resulting in mutations at the damage site.
authors.affiliation: Department of Chemistry and Biochemistry, Queens College, City University of New York, Flushing, New York 11367, USA.
authors.forename: R B
authors.initials: RB
authors.lastname: Greenberg
authors.forename: M
authors.initials: M
authors.lastname: Alberti
authors.forename: J E
authors.initials: JE
authors.lastname: Hearst
authors.forename: M A
authors.initials: MA
authors.lastname: Chua
authors.forename: W A
authors.initials: WA
authors.lastname: Saffran
mesh_terms: D001483:Base Sequence; D017931:DNA Primers; D004260:DNA Repair; D011564:Furocoumarins / Q000633:toxicity*; D005800:Genes, Fungal; D009153:Mutagens / Q000633:toxicity*; D011995:Recombination, Genetic; D012441:Saccharomyces cerevisiae / Q000187:drug effects* / Q000235:genetics
chemical_list: D017931:DNA Primers; D011564:Furocoumarins; D009153:Mutagens