Identification of a subunit of a novel Kleisin-beta/SMC complex as a potential substrate of protein phosphatase 2A.
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.
Yeong
Foong May
FM
Institute of Medical Biochemistry, Division of Molecular Biology, Vienna Biocenter, University of Vienna, Dr. Bohr-Gasse 9, A-1030 Vienna, Austria.
Hombauer
Hans
H
Wendt
Kerstin S
KS
Hirota
Toru
T
Mudrak
Ingrid
I
Mechtler
Karl
K
Loregger
Thomas
T
Marchler-Bauer
Aron
A
Tanaka
Koichi
K
Peters
Jan-Michael
JM
Ogris
Egon
E
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
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D046912:Multiprotein Complexes; C108312:condensin complexes; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D000251:Adenosine Triphosphatases