How do cells coordinate the processes of chromosome segregation and cell division? To better understand this issue we have been studying the classic temperature-sensitive sterile-uncoordinated mutant,
stu-4. In
stu-4 (
e2406) mutants, cells undergo multiple rounds of normal DNA replication and centrosome duplication, but are aberrant in chromosome segregation and cell division resulting in the formation of polyploid cells. However, there is no apparent delay in the progress of subsequent cell cycles. Furthermore, the defect is not restricted to mitotic cells since meiosis is affected as well. The
stu-4 gene encodes a protein with homology to the separins, an emerging class of proteases, which act at the Metaphase to Anaphase transition to cleave the cohesins that hold sister-chromatids together. A second function in Anaphase B spindle movement was also shown recently in S. cerevisiae. We are interested in understanding the function of this protein in a higher metazoan since there are subtle but important differences in the mechanisms of chromosome segregation and cell division between them and yeast.