Gene products required for mitotic chromosome separation in the fission yeast Schizosaccharomyces pombe are described. They have been identified by two distinct strategies of mutant isolation, followed by gene cloning and immunochemical characterization of gene products. The roles of four representative genes, namely nda3+, nuc2+, top2+ and dis2+, encoding beta-tubulin, a nuclear scaffold-like protein, DNA topoisomerase II and type-1 protein phosphatase, respectively, are discussed in regard to the mechanisms and control of chromosome separation.