Ase1 GFP somewhat colocalized with Spc29 CFP in 7-8ft of smallbudded cells with unseparated SPBs and was not detectable within the remaining cells. Though this staining may reveal Ase1 localization to the intranuclear MTs, it is difficult to specifically determine whether Ase1 localizes to the SPBs or the nuclear MTs in these cells since the nuclear MTs are short ahead of spindle assembly. Regardless, the appearance of Ase1 temporally precedes SPB separation, consistent with a role for Ase1 in spindle assembly. We next analyzed Ase1GFP (-)-MK 801 in ipl1 315 cells and discovered that, contrary to 7-8ft of the wild type cells, it had been just apparent in 54% of the ipl1 315 small budded cells. Ipl1 therefore regulates the localization of Ase1 at the time of spindle assembly, consistent with these proteins working together to control spindle assembly. Bi-polar spindle assembly is important for chromosome segregation and requires the activity of the BimC kinesins, a conserved family of plus end motor proteins. In budding yeast, the Cin8 and Kip1 BimC kinesins act in parallel Organism spindle assembly paths, with Cin8 making the important contribution to spindle assembly. Here we report that the Ipl1 protein kinase and the spindle midzone protein Ase1 also become needed for spindle assembly in the lack of Cin8. A Separation of Function Allele Reveals a Role for Ipl1/Aurora in Spindle Assembly Surprisingly, our examination of the ipl1 315 allele that’s lethal in the absence of cin8 decided that it is experienced in all of the previously determined MT based capabilities of Ipl1. While cin8 mutants arrest in mitosis due to spindle checkpoint activation, the inviability of cin8 ipl1 315 cells was not due to deficiencies in checkpoint exercise. Alternatively, cin8 ipl1 315 double mutants arrest with duplicated but unseparated SPBs. The necessity for Ipl1 to put together spindles in nature products the lack of Cin8 is not unique to ipl1 315 since the ipl1 321 mutation can also be lethal with cin8 mutants. Nevertheless, to our understanding this is the first case of an ipl1 mutant that’s specifically defective in mere among the known Ipl1 features. Ipl1 315 includes a single mutation in the catalytic domain, leading to paid down kinase activity. We propose that the interaction contributes to the decrease in Ipl1 kinase activity, because Ipl1315 also demonstrated a decreased interaction with its activator, Sli15. Since all other mutants we’ve examined also have reduced kinase activity, we were surprised the lowering of kinase activity did not affect other Ipl1 features. However, Ipl1 315 holds 2 fold more kinase activity than Ipl1 321, indicating that higher levels of Ipl1 kinase activity are needed for its spindle construction purpose than for its other characteristics, probably because of limiting substrate.