title: Cloning and characterization of the parC and parE genes of Streptococcus pneumoniae encoding DNA topoisomerase IV: role in fluoroquinolone resistance.
abstract: DNA topoisomerase IV mediates chromosome segregation and is a potential target for antibacterial agents including new antipneumococcal fluoroquinolones. We have used hybridization to a Staphylococcus aureus gyrB probe in concert with chromosome walking to isolate the Streptococcus pneumoniae parE-parC locus, lying downstream of a putative new insertion sequence and encoding 647-residue ParE and 823-residue ParC subunits of DNA topoisomerase IV. These proteins exhibited greatest homology respectively to the GrlB (ParE) and GrlA (ParC) subunits of S. aureus DNA topoisomerase IV. When combined, whole-cell extracts of Escherichia coli strains expressing S. pneumoniae ParC or ParE proteins reconstituted a salt-insensitive ATP-dependent decatenase activity characteristic of DNA topoisomerase IV. A second gyrB homolog isolated from S. pneumoniae encoded a 648-residue protein which we identified as GyrB through its close homology both to counterparts in S. aureus and Bacillus subtilis and to the product of the S. pneumoniae nov-1 gene that confers novobiocin resistance. gyrB was not closely linked to gyrA. To examine the role of DNA topoisomerase IV in fluoroquinolone action and resistance in S. pneumoniae, we isolated mutant strains stepwise selected for resistance to increasing concentrations of ciprofloxacin. We analysed four low-level resistant mutants and showed that Ser-79 of ParC, equivalent to resistance hotspots Ser-80 of GrlA and Ser-84 of GyrA in S. aureus, was in each case substituted with Tyr. These results suggest that DNA topoisomerase IV is an important target for fluoroquinolones in S. pneumoniae and establish this organism as a useful gram-positive system for resistance studies.
authors.affiliation: Molecular Genetics Group, Department of Cellular and Molecular Sciences, St. George's Hospital Medical School, University of London, United Kingdom.
authors.forename: X S
authors.initials: XS
authors.lastname: Pan
authors.forename: L M
authors.initials: LM
authors.lastname: Fisher
mesh_terms: D000595:Amino Acid Sequence; D000890:Anti-Infective Agents / Q000494:pharmacology*; D001483:Base Sequence; D002939:Ciprofloxacin / Q000494:pharmacology*; D003001:Cloning, Molecular; D027081:DNA Gyrase; D027101:DNA Topoisomerase IV; D004250:DNA Topoisomerases, Type II / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D004251:DNA Transposable Elements; D004352:Drug Resistance, Microbial / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D011994:Recombinant Proteins / Q000378:metabolism; D015183:Restriction Mapping; D012641:Selection, Genetic; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013296:Streptococcus pneumoniae / Q000187:drug effects / Q000201:enzymology / Q000235:genetics*
chemical_list: D000890:Anti-Infective Agents; D004251:DNA Transposable Elements; D011994:Recombinant Proteins; D002939:Ciprofloxacin; D027101:DNA Topoisomerase IV; D027081:DNA Gyrase; D004250:DNA Topoisomerases, Type II