Morphological changes of the mitotic spindle are tightly regulated by the cell cycle surveillance machinery. Since mitotic kinesin-related proteins play an important role in spindle dynamics, it was suggested that their activity is also regulated throughout the cell cycle. However, there was no experimental data to support this assumption. In our research we found that Cin8 is differentially phosphorylated at the end of anaphase and that in vitro activity of Cin8 is modified during the course of mitosis. We are currently exploring the molecular mechanisms that underlie this change in activity.
     S. cerevisiae anaphase B spindle elongation proceeds through the overlapping function of three molecular motors: Cin8, Kip1, and dynein. To explore the mechanism of overlap between these three motors, we examine spindle and microtubule dynamics in cin8 mutant strains, expressed either alone or in the background of KIP1 and DYN1 deletions. By these experiments we identify specific roles of Cin8 that overlap with Kip1 and dynein.

Anaphase spindle localization of Cin8 is regulated by phosphorylation
Top: Time-lapse sequence of spindle localization of Wild-type Cin8-3GFP.
Bottom: Time-lapse sequence of spindle localization of phosphorylation deficient Cin8-3A-GFP. In this mutant, the three Cdk1 sites in the catalytic domain (S277, T285, S493) were mutated to alanine. Time interval between frames is 1 minute. Bar- 1 micrometer.
While the WT Cin8 detaches from the spindle at late anaphase, the phosphorylation deficient Cin8 variant remains attached to the kinetochores and the midzone.