title: Identification of a subunit of a novel Kleisin-beta/SMC complex as a potential substrate of protein phosphatase 2A.
abstract: Protein phosphatase 2A (PP2A) holoenzymes consist of a catalytic C subunit, a scaffolding A subunit, and one of several regulatory B subunits that recruit the AC dimer to substrates. PP2A is required for chromosome segregation, but PP2A's substrates in this process remain unknown. To identify PP2A substrates, we carried out a two-hybrid screen with the regulatory B/PR55 subunit. We isolated a human homolog of C. elegans HCP6, a protein distantly related to the condensin subunit hCAP-D2, and we named this homolog hHCP-6. Both C. elegans HCP-6 and condensin are required for chromosome organization and segregation. HCP-6 binding partners are unknown, whereas condensin is composed of the structural maintenance of chromosomes proteins SMC2 and SMC4 and of three non-SMC subunits. Here we show that hHCP-6 becomes phosphorylated during mitosis and that its dephosphorylation by PP2A in vitro depends on B/PR55, suggesting that hHCP-6 is a B/PR55-specific substrate of PP2A. Unlike condensin, hHCP-6 is localized in the nucleus in interphase, but similar to condensin, hHCP-6 associates with chromosomes during mitosis. hHCP-6 is part of a complex that contains SMC2, SMC4, kleisin-beta, and the previously uncharacterized HEAT repeat protein FLJ20311. hHCP-6 is therefore part of a condensin-related complex that associates with chromosomes in mitosis and may be regulated by PP2A.
authors.affiliation: Institute of Medical Biochemistry, Division of Molecular Biology, Vienna Biocenter, University of Vienna, Dr. Bohr-Gasse 9, A-1030 Vienna, Austria.
authors.forename: Foong May
authors.initials: FM
authors.lastname: Yeong
authors.forename: Hans
authors.initials: H
authors.lastname: Hombauer
authors.forename: Kerstin S
authors.initials: KS
authors.lastname: Wendt
authors.forename: Toru
authors.initials: T
authors.lastname: Hirota
authors.forename: Ingrid
authors.initials: I
authors.lastname: Mudrak
authors.forename: Karl
authors.initials: K
authors.lastname: Mechtler
authors.forename: Thomas
authors.initials: T
authors.lastname: Loregger
authors.forename: Aron
authors.initials: A
authors.lastname: Marchler-Bauer
authors.forename: Koichi
authors.initials: K
authors.lastname: Tanaka
authors.forename: Jan-Michael
authors.initials: JM
authors.lastname: Peters
authors.forename: Egon
authors.initials: E
authors.lastname: Ogris
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002874:Chromosome Mapping; D020090:Chromosome Segregation / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D015151:Immunoblotting; D046912:Multiprotein Complexes; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010766:Phosphorylation; D011233:Precipitin Tests; D054648:Protein Phosphatase 2; D013379:Substrate Specificity
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D046912:Multiprotein Complexes; C108312:condensin complexes; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D000251:Adenosine Triphosphatases