title: Byr4 and Cdc16 form a two-component GTPase-activating protein for the Spg1 GTPase that controls septation in fission yeast.
abstract: BACKGROUND
  Spatial and temporal control of cytokinesis ensures the accurate transmission of genetic material and the correct development of multicellular organisms. An excellent model system in which to study cytokinesis is Schizosaccharomyces pombe because there are similarities between cytokinesis in S. pombe and mammals and because genes involved in S. pombe cytokinesis have been characterized. In particular, formation of the septum is positively regulated by the Spg1 GTPase and its effector, the Cdc7 kinase. Septation is negatively regulated by Cdc16, a protein similar to GTPase-activating proteins (GAPs) for Ypt GTPases, and by Byr4, a protein of unknown biochemical function. This study investigates the relationship between Byr4, Cdc16, and Spg1.
  
  
  RESULTS
  Genetic interactions were observed between byr4, cdc16, and spg1 mutants. Byr4 bound to Cdc16 and Spg1 in yeast two-hybrid assays and in coprecipitations in vitro and in yeast. Byr4 inhibited the dissociation and hydrolysis of GTP bound to Spg1, but when Byr4 and Cdc16 were combined together they displayed Spg1GAP activity in vitro; Cdc16 alone had no detectable GAP activity. The binding of Byr4 to Spg1 and the Byr4-Cdc16 Spg1GAP activity were specific because Byr4 and Cdc16 did not bind to or affect the GTPase activities of the seven known S pombe Ypt family GTPase.
  
  
  CONCLUSIONS
  Byr4 and Cdc16 form a two-component GAP for the Spg1 GTPase. Byr4 and Cdc16 appear to negatively regulate septation in S. pombe by modulating the nucleotide state of Spg1 possibly in a spatially or temporally controlled manner.
authors.affiliation: Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA.
authors.forename: K A
authors.initials: KA
authors.lastname: Furge
authors.forename: K
authors.initials: K
authors.lastname: Wong
authors.forename: J
authors.initials: J
authors.lastname: Armstrong
authors.forename: M
authors.initials: M
authors.lastname: Balasubramanian
authors.forename: C F
authors.initials: CF
authors.lastname: Albright
mesh_terms: D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002455:Cell Division; D004789:Enzyme Activation; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D020558:GTP Phosphohydrolases / Q000235:genetics / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism; D006868:Hydrolysis; D009154:Mutation; D011485:Protein Binding; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D012568:Schizosaccharomyces / Q000166:cytology* / Q000201:enzymology; D029702:Schizosaccharomyces pombe Proteins
chemical_list: C100413:Byr4 protein, S pombe; D018797:Cell Cycle Proteins; D005656:Fungal Proteins; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D029702:Schizosaccharomyces pombe Proteins; C498281:cdc16 protein, S pombe; D006160:Guanosine Triphosphate; D020558:GTP Phosphohydrolases