Cell cycle-dependent phosphorylation, nuclear localization, and activation of human condensin.
Condensin, one of the most abundant components of mitotic chromosomes, is a conserved protein complex composed of two structural maintenance of chromosomes (SMC) subunits (SMC2- and SMC4-type) and three non-SMC subunits, and it plays an essential role in mitotic chromosome condensation. Purified condensin reconfigures DNA structure using energy provided by ATP hydrolysis. To know the regulation of condensin in somatic cells, the expression level, subcellular localization, and phosphorylation status of human condensin were examined during the cell cycle. The levels of condensin subunits were almost constant throughout the cell cycle, and the three non-SMC subunits were phosphorylated at specific sites in mitosis and dephosphorylated upon the completion of mitosis. Subcellular fractionation studies revealed that a proportion of condensin was tightly bound to mitotic chromosomes and that this form was phosphorylated at specific sites. Condensin purified from mitotic cells had much stronger supercoiling activity than that purified from interphase cells. These results suggest that condensin functions in somatic cells are regulated by phosphorylation in two ways during the cell cycle; the phosphorylation of specific sites correlates with the chromosomal targeting of condensin, and its biochemical activity is stimulated by phosphorylation.
Takemoto
Ai
A
Cellular Physiology Laboratory, Discovery Research Institute, RIKEN, Japan Science and Technology Corp., 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
Kimura
Keiji
K
Yokoyama
Shigeyuki
S
Hanaoka
Fumio
F
D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D001665:Binding Sites; D002453:Cell Cycle / Q000502:physiology*; D002467:Cell Nucleus / Q000378:metabolism; D002868:Chromosomal Proteins, Non-Histone / Q000737:chemistry / Q000378:metabolism*; D002875:Chromosomes / Q000378:metabolism; D004278:DNA, Superhelical / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D004789:Enzyme Activation; D004795:Enzyme Stability; D006367:HeLa Cells; D006801:Humans; D008938:Mitosis; D046912:Multiprotein Complexes; D010766:Phosphorylation; D021122:Protein Subunits
D002868:Chromosomal Proteins, Non-Histone; D004278:DNA, Superhelical; D004268:DNA-Binding Proteins; D046912:Multiprotein Complexes; D021122:Protein Subunits; C108312:condensin complexes; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; C580922:SMC4 protein, human