The IML3/MCM19 gene of Saccharomyces cerevisiae is required for a kinetochore-related process during chromosome segregat
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O R I GI N A L P A P E R
S. K. Ghosh á A. Poddar á S. Hajra K. Sanyal á P. Sinha
The IML3/ MCM19 gene of Saccharomyces cerevisiae is required for a kinetochore-related process during chromosome segregation Received: 2 May 2000 / Accepted: 9 November 2000 / Published online: 19 January 2001 Ó Springer-Verlag 2001
Abstract The mcm19 mutation in budding yeast aects minichromosome maintenance. In this work we have shown that this mutation leads to defects in the segregation of minichromosomes and chromosomes. The mutant cells show defective kinetochore function as judged by three criteria ± relaxation of the transcriptional block normally associated with a CEN box, stable maintenance of a dicentric plasmid in mutant cells, and mild sensitivity to the antimicrotubule drug benomyl. The MCM19 gene has been cloned and found to be the same as IML3, which codes for the ORF YBR107C. Deletion of the gene was not lethal, nor did it confer any growth defects on the mutant cells. However, the mcm19 null mutation conferred growth defects in the presence of a mutation in the TUB1 gene coding for alphatubulin. Two-hybrid experiments showed an interaction between Iml3p/Mcm19p and the kinetochore protein Chl4, indicating that the Iml3/Mcm19 protein has a role in kinetochore function. Key words iml á mcm á Chromosome segregation á Kinetochores á Yeast
Communicated by C. P. Hollenberg S. K. Ghosh á A. Poddar1 á S. Hajra á K. Sanyal2 á P. Sinha (&) Department of Biochemistry, Bose Institute, P1/12 CIT Scheme VII M, Calcutta 700 054, India E-mail: [email protected] Tel.: +91-33-3379544 Fax: +91-33-3343886 Present addresses: Department of Biochemistry and Molecular Genetics, University of Virginia Medical Center, Charlottesville, VA 22908-0733, USA 1
2 Division of Biology, University of California, Santa Barbara, CA 93106, USA
The ®rst two authors have contributed equally to this work
Introduction Faithful replication and segregation of chromosomes are two major events of a successful cell division cycle. If either of these two events fails to occur with high ®delity, the result may be cell cycle arrest, propagation of aneuploidy or even cell death. The budding yeast Saccharomyces cerevisiae is a model eukaryote for a study of both these processes. The centromere of a chromosome is the site where proteins assemble to form a kinetochore complex. This complex is responsible for capturing microtubules, allowing the sister chromatids to get attached to microtubules coming from opposite spindle poles. When a kinetochore fails to attach to the microtubule or forms weak interactions with it, the chromatids may fail to move to opposite poles and chromosome non-disjunction occurs, leading to the loss of the chromosome from one of the daughter cells and gain in the other. Therefore, cells which exhibit chromosome non-disjunction could carry mutations in genes which are required for the proper functioning of the kinetochores. In the budding yeast, the centromere consists of about 125 base pairs of DNA divided into three tandem boxes ±
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