The spindle pole body in Saccharomyces cerevisiae is a dynamic structure

The spindle pole body (SPB) in the budding yeast Saccharomyces cerevisiae is the sole microtubule organizer in the cell. The SPB is a macromolecular cylindrical structure that spans the nuclear envelope and initiates microtubule nucleation in the nucleus and cytoplasm. The SPB is composed of electron-dense layers arranged in a stack. The central plaque is anchored in the plane of the nuclear envelope, the inner plaque nucleates the spindle microtubules in the nucleus and the outer plaque nucleates the cytoplasmic microtubules in the cytoplasm.; During SPB duplication, the new SPB is assembled at a distinct site adjacent to the old SPB. Using quantitative fluorescence methods, I studied the assembly and dynamics of the core structural SPB component Spc110p. The SPB core exhibits both exchange and growth in a cell-cycle-dependent fashion. During G1/S phase, the old SPB exchanges about 50% of old Spc110p for new Spc110p. In G2 little Spc110p is exchangeable. Thus Spc110p is dynamic during G1/S and becomes stable during G2. The SPB incorporates additional Spc110p in late G2 and M phases; this growth is followed by reduction in the next G1. Spc110p addition to the SPBs (growth) also occurs in response to G2 and mitotic arrests but not during a G1 arrest. My results reveal several dynamic features of the SPB core: cell-cycle-dependent growth and reduction, growth in response to cell cycle arrests, and exchange of Spc110p during SPB duplication. Moreover, rather than being considered a conservative or dispersive process, the assembly of Spc110p into the SPB is more readily considered in terms of growth and exchange.