A novel nucleolar protein, NIFK, interacts with the forkhead associated domain of Ki-67 antigen in mitosis

J Biol Chem. 2001 Jul 6;276(27):25386-91. doi: 10.1074/jbc.M102227200. Epub 2001 May 7.


In a previous study, we demonstrated that the forkhead associated (FHA) domain of pKi-67 interacts with the novel kinesin-like protein, Hklp2 (Sueishi, M., Takagi, M., and Yoneda, Y. (2000) J. Biol. Chem. 275, 28888-28892). In this study, we report on the identification of a putative RNA-binding protein of 293 residues as another binding partner of the FHA domain of pKi-67 (referred to as NIFK for nucleolar protein interacting with the FHA domain of pKi-67). Human NIFK (hNIFK) interacted with the FHA domain of pKi-67 (Ki-FHA) efficiently in vitro when hNIFK was derived from mitotically arrested cells. In addition, a moiety of hNIFK was co-localized with pKi-67 at the peripheral region of mitotic chromosomes. The hNIFK domain that interacts with Ki-FHA was mapped in the yeast two-hybrid system to a portion encompassed by residues 226-269. In a binding assay utilizing Xenopus egg extracts, it was found that the mitosis-specific environment and two threonine residues within this portion of hNIFK (Thr-234 and Thr-238) were crucial for the efficient interaction of hNIFK and Ki-FHA, suggesting that hNIFK interacts with Ki-FHA in a mitosis-specific and phosphorylation-dependent manner. These findings provide a new clue to our understanding of the cellular function of pKi-67.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Binding Sites
  • Carrier Proteins / chemistry
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism*
  • Cell Cycle
  • Cloning, Molecular
  • Drosophila Proteins*
  • HeLa Cells
  • Humans
  • Insect Proteins / chemistry*
  • Intracellular Signaling Peptides and Proteins*
  • Ki-67 Antigen / chemistry
  • Ki-67 Antigen / metabolism*
  • Mice
  • Microfilament Proteins
  • Mitosis*
  • Molecular Sequence Data
  • Nuclear Proteins / chemistry
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism*
  • Peptide Mapping
  • Phosphorylation
  • Protein Binding
  • RNA-Binding Proteins
  • Threonine / metabolism


  • Carrier Proteins
  • Drosophila Proteins
  • Insect Proteins
  • Intracellular Signaling Peptides and Proteins
  • Ki-67 Antigen
  • Microfilament Proteins
  • NIFK protein, human
  • NIFK protein, mouse
  • Nuclear Proteins
  • RNA-Binding Proteins
  • f protein, Drosophila
  • Threonine

Associated data

  • GENBANK/AB044971
  • GENBANK/AB056870