title: SCT1 mutants suppress the camptothecin sensitivity of yeast cells expressing wild-type DNA topoisomerase I.
abstract: Camptothecin is a potent antineoplastic agent that interferes with the action of eukaryotic DNA topoisomerase I; the covalent enzyme-DNA intermediate is reversibly stabilized, leading to G2 arrest and cell death. We used a genetic screen to identify cellular factors, other than DNA topoisomerase I, that participate in the process of camptothecin-induced cell death. Following ethyl methanesulfonate mutagenesis of top1 delta yeast cells expressing plasmid-borne wild-type DNA topoisomerase I, six dominant suppressors of camptothecin toxicity were isolated that define a single genetic locus, sct1. Mutant SCT1 cells expressed DNA topoisomerase I protein of similar specific activity and camptothecin sensitivity to that of congenic, drug-sensitive sct1 cells, yet were resistant to camptothecin-mediated lethality. Moreover, camptothecin-treated SCT1 cells did not exhibit the G2-arrested, terminal phenotype characteristic of drug-treated wild-type cells. SCT1 cell sensitivity to other DNA-damaging agents suggests that alterations in SCT1 function suppress camptothecin-induced DNA damage produced in the presence of yeast DNA topoisomerase I.
authors.affiliation: Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, PA 19107, USA.
authors.forename: E A
authors.initials: EA
authors.lastname: Kauh
authors.forename: M A
authors.initials: MA
authors.lastname: Bjornsti
mesh_terms: D002166:Camptothecin / Q000494:pharmacology*; D002453:Cell Cycle; D004264:DNA Topoisomerases, Type I / Q000096:biosynthesis* / Q000302:isolation & purification; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D005020:Ethyl Methanesulfonate / Q000494:pharmacology; D005656:Fungal Proteins / Q000235:genetics*; D015870:Gene Expression; D007700:Kinetics; D016296:Mutagenesis; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics* / Q000502:physiology; D013045:Species Specificity; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism
chemical_list: D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D014157:Transcription Factors; D005020:Ethyl Methanesulfonate; D004264:DNA Topoisomerases, Type I; D002166:Camptothecin