title: Arabidopsis thaliana GYRB3 does not encode a DNA gyrase subunit.
abstract: BACKGROUND
  DNA topoisomerases are enzymes that control the topology of DNA in all cells. DNA gyrase is unique among the topoisomerases in that it is the only enzyme that can actively supercoil DNA using the free energy of ATP hydrolysis. Until recently gyrase was thought to be unique to bacteria, but has now been discovered in plants. The genome of the model plant, Arabidopsis thaliana, is predicted to encode four gyrase subunits: AtGyrA, AtGyrB1, AtGyrB2 and AtGyrB3.
  
  
  RESULTS
  We found, contrary to previous data, that AtGyrB3 is not essential to the survival of A. thaliana. Bioinformatic analysis suggests AtGyrB3 is considerably shorter than other gyrase B subunits, lacking part of the ATPase domain and other key motifs found in all type II topoisomerases; but it does contain a putative DNA-binding domain. Partially purified AtGyrB3 cannot bind E. coli GyrA or support supercoiling. AtGyrB3 cannot complement an E. coli gyrB temperature-sensitive strain, whereas AtGyrB2 can. Yeast two-hybrid analysis suggests that AtGyrB3 cannot bind to AtGyrA or form a dimer.
  
  
  CONCLUSIONS
  These data strongly suggest that AtGyrB3 is not a gyrase subunit but has another unknown function. One possibility is that it is a nuclear protein with a role in meiosis in pollen.
authors.affiliation: Department of Biological Chemistry, John Innes Centre, Norwich, United Kingdom.
authors.forename: Katherine M
authors.initials: KM
authors.lastname: Evans-Roberts
authors.forename: Christian
authors.initials: C
authors.lastname: Breuer
authors.forename: Melisa K
authors.initials: MK
authors.lastname: Wall
authors.forename: Keiko
authors.initials: K
authors.lastname: Sugimoto-Shirasu
authors.forename: Anthony
authors.initials: A
authors.lastname: Maxwell
mesh_terms: D020816:Amino Acid Motifs; D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000502:physiology*; D019295:Computational Biology; D027081:DNA Gyrase / Q000378:metabolism*; D026942:DNA Topoisomerases / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology*; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D008540:Meiosis; D009687:Nuclear Proteins / Q000378:metabolism; D010641:Phenotype; D018521:Plant Physiological Phenomena; D011058:Pollen / Q000378:metabolism; D011487:Protein Conformation; D020798:Two-Hybrid System Techniques
chemical_list: D029681:Arabidopsis Proteins; D004268:DNA-Binding Proteins; C554843:GyrB3 protein, Arabidopsis; D009687:Nuclear Proteins; D026942:DNA Topoisomerases; D027081:DNA Gyrase