MIF2 IS REQUIRED FOR MITOTIC SPINDLE INTEGRITY DURING ANAPHASE SPINDLE ELONGATION IN SACCHAROMYCES-CEREVISIAE

The function of the essential MIF2 gene in the Saccharomyces cerevisia e cell cycle was examined by overexpressing or creating a deficit of M IF2 gene product. When MIF2 was overexpressed, chromosomes missegregat ed during mitosis and cells accumulated in the G2 and M phases of the cell cycle. Temperature sensitive mutants isolated by in vitro mutagen esis delayed cell cycle progression when grown at the restrictive temp erature, accumulated as large budded cells that had completed DNA repl ication but not chromosome segregation, and lost viability as they pas sed through mitosis. Mutant cells also showed increased levels of mito tic chromosome loss, supersensitivity to the microtubule destabilizing drug MBC, and morphologically aberrant spindles. mif2 mutant spindles arrested development immediately before anaphase spindle elongation, and then frequently broke apart into two disconnected short half spind les with misoriented spindle pole bodies. These findings indicate that MIF2 is required for structural integrity of the spindle during anaph ase spindle elongation. The deduced Mif2 protein sequence shared no ex tensive homologies with previously identified proteins but did contain a short region of homology to a motif involved in binding AT rich DNA by the Drosophila D1 and mammalian HMGI chromosomal proteins.