The yeast type I topoisomerase Top3 interacts with Sgs1, a DNA helicase homolog: a potential eukaryotic reverse gyrase.
We have previously shown that cells mutant for TOP3, a gene encoding a prokaryotic-like type I topoisomerase in Saccharomyces cerevisiae, display a pleiotropic phenotype including slow growth and genome instability. We identified a mutation, sgs1 (slow growth suppressor), that suppresses both the growth defect and the increased genomic instability of top3 mutants. Here we report the independent isolation of the SGS1 gene in a screen for proteins that interact with Top3. DNA sequence analysis reveals that the putative Sgs1 protein is highly homologous to the helicase encoded by the Escherichia coli recQ gene. These results imply that Sgs1 creates a deleterious topological substrate that Top3 preferentially resolves. The interaction of the Sgs1 helicase homolog and the Top3 topoisomerase is reminiscent of the recently described structure of reverse gyrase from Sulfolobus acidocaldarius, in which a type I DNA topoisomerase and a helicase-like domain are fused in a single polypeptide.
Department of Genetics and Development, College of Physicians and Surgeons, Columbia University, New York, New York 10032.
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S
Gangloff
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JP
McDonald
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C
Bendixen
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L
Arthur
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Rothstein
D000595:Amino Acid Sequence; D001483:Base Sequence; D002453:Cell Cycle; D003001:Cloning, Molecular; D004265:DNA Helicases / Q000737:chemistry; D017931:DNA Primers / Q000737:chemistry; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D005800:Genes, Fungal; D016153:Genes, Suppressor; D008969:Molecular Sequence Data; D011485:Protein Binding; D053484:RecQ Helicases; D011995:Recombination, Genetic; D015183:Restriction Mapping; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D029701:Saccharomyces cerevisiae Proteins; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
D017931:DNA Primers; D005656:Fungal Proteins; D029701:Saccharomyces cerevisiae Proteins; C090472:SGS1 protein, S cerevisiae; D004265:DNA Helicases; D053484:RecQ Helicases; D004264:DNA Topoisomerases, Type I