The IML3/MCM19 gene of Saccharomyces cerevisiae is required for a kinetochore-related process during chromosome segregation

Abstract.

The mcm19 mutation in budding yeast affects 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 alpha-tubulin. 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.