Ibd1p, a possible spindle pole body associated protein, regulates nuclear division and bud separation in Saccharomyces cerevisiae

Jeongkyo Lee, Hyung Seo Hwang, Jinmi Kim, Kiwon Song

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15 Citations (Scopus)


The proper spatial and temporal coordination of mitosis and cytokinesis is essential for maintaining genomic integrity. We describe the identification and characterization of the Saccharomyces cerevisiae IBD1 gene, which encodes a novel protein that regulates the proper nuclear division and bud separation. IBD1 was identified by the limited homology to byr4, a dosage-dependent regulator of cytokinesis in Schizosaccharomyces pombe. IBD1 is not an essential gene, and the knock-out cells show no growth defects except for the reduced mating efficiency [1]. However, upon ectopic expression from an inducible promoter, IBD1 is lethal to the cell and leads to abnormal nuclear division and bud separation. In detail, approximately 90% of the IBD1 overexpressing cells arrest at large bud stages with dividing or divided nuclei. In some IBD1 overexpressing cells, spindle elongation and chromosome separation occur within the mother cell, leading to anucleated and binucleate daughter cells. The anucleated cell can not bud, but the binucleate cell proceeds through another cell cycle(s) to produce a cell with multiple nuclei and multiple buds. Observations of the F-actin and chitin rings in the IBD1 overexpressing cells reveal that these cells lose the polarity for bud site selection and growth or attain the hyper-polarity for growth. Consistent with the phenotypes, the IBD1 overexpressing cells contain a broad range of DNA content, from 2 to 4 N or more. A functional Ibd1p-GFP fusion protein localizes to a single dot at the nuclear DNA boundary in the divided nuclei or to double dots in dividing nuclei, suggesting its localization on the spindle pole body (SPB). The cross-species expressions of IBD1 in S. pombe and byr4 in S. cerevisiae cause defects in shape, implicating the presence of a conserved mechanism for the control of cytokinesis in eukaryotes. We propose that Ibd1p is an SPB associated protein that links proper nuclear division to cytokinesis and bud separation. Copyright (C) 1999 Elsevier Science B.V.

Original languageEnglish
Pages (from-to)239-253
Number of pages15
JournalBiochimica et Biophysica Acta - Molecular Cell Research
Issue number3
Publication statusPublished - 1999 Apr 1

Bibliographical note

Funding Information:
We thank Dr. M. Huang and Dr. F. Galibert (Laboratoire de Biochimie et Biologie Moleculaire, France) for YJR053W knock-out strains, J.C. Yoo (Catholic University, Korea) for S. cerevisiae strains and pMW20, C. Albright and K. Gould (Vanderbilt University, Nashville, TN) for S. pombe strains and plasmids, H. Mosch for pRS316-gfp plasmid, and K.-Y. Choi for the alpha factor (Yonsei University, Korea). We are also grateful to H.S. Choi for technical help in cloning pMW20/IBD1C, to H.S. Lee for FACS analyses (Yonsei University, Medical College, FACS Facility) and to J.H. Song and K.S. Lee for their help in computer image analyses (Yonsei University, Korea). This work was funded by Grants from the Genetic Engineering Program of 1998, Ministry of Education, Republic of Korea, and the Yonsei University Research Fund of 1997 given to K. Song.

All Science Journal Classification (ASJC) codes

  • Molecular Biology
  • Cell Biology

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