title: Identification of a topoisomerase I mutant, scsA1, as an extragenic suppressor of a mutation in scaA(NBS1), the apparent homolog of human nibrin in Aspergillus nidulans.
abstract: The Mre11-Rad50-Nbs1 protein complex has emerged as a central player in the human cellular DNA damage response, and recent observations suggest that these proteins are at least partially responsible for the linking of DNA damage detection to DNA repair and cell cycle checkpoint functions. Mutations in scaA(NBS1), which encodes the apparent homolog of human nibrin in Aspergillus nidulans, inhibit growth in the presence of the antitopoisomerase I drug camptothecin. This article describes the selection and characterization of extragenic suppressors of the scaA1 mutation, with the aim of identifying other proteins that interfere with the pathway or complex in which the ScaA would normally be involved. Fifteen extragenic suppressors of the scaA1 mutation were isolated. The topoisomerase I gene can complement one of these suppressors. Synergistic interaction between the scaA(NBS1) and scsA(TOP1) genes in the presence of DNA-damaging agents was observed. Overexpression of topoisomerase I in the scaA1 mutant causes increased sensitivity to DNA-damaging agents. The scsA(TOP1) and the scaA(NBS1) gene products could functionally interact in pathways that either monitor or repair DNA double-strand breaks.
authors.affiliation: Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, CEP 14040-903 São Paulo, Brazil.
authors.forename: Marcia R Z Kress
authors.initials: MR
authors.lastname: Fagundes
authors.forename: Larissa
authors.initials: L
authors.lastname: Fernandes
authors.forename: Marcela
authors.initials: M
authors.lastname: Savoldi
authors.forename: Steven D
authors.initials: SD
authors.lastname: Harris
authors.forename: Maria H S
authors.initials: MH
authors.lastname: Goldman
authors.forename: Gustavo H
authors.initials: GH
authors.lastname: Goldman
mesh_terms: D001233:Aspergillus nidulans; D001483:Base Sequence; D002166:Camptothecin; D018797:Cell Cycle Proteins / Q000235:genetics*; D003433:Crosses, Genetic; D017931:DNA Primers; D004260:DNA Repair / Q000235:genetics*; D004264:DNA Topoisomerases, Type I / Q000235:genetics*; D024202:Electrophoretic Mobility Shift Assay; D005656:Fungal Proteins / Q000235:genetics*; D015870:Gene Expression; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009154:Mutation / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D013489:Suppression, Genetic / Q000235:genetics*
chemical_list: D018797:Cell Cycle Proteins; D017931:DNA Primers; D005656:Fungal Proteins; C428908:scaA protein, Aspergillus; D004264:DNA Topoisomerases, Type I; D002166:Camptothecin