FIGURE 7:

Mzt1 plays a role in the activation of the γTuRC ring but not the γTuSC ring. (A) Mzt1 overproduction has no effect on alp16Δ cells but increases the spindle microtubule level without increasing the level of γTuC at mitotic SPBs in wild-type cells. Mzt1 was overproduced at the lys1 locus under the control of P41nmt in the absence of thiamine at 27ºC for 22 h in wild-type and alp16Δ cells containing GFP-Alp4^GCP2 and mCh-Atb2. Alp4^GCP2 and Atb2 levels for spindles <3.5 μm in length were quantified. (B) The ratio of Mzt1 to γTuC increases at early M phase in wild-type cells. The ratio of Mzt1 to Alp4^GCP2 level at mitotic SPBs was calculated in wild-type and alp16Δ cells from the data shown in Figure 1, D and E, and plotted against spindle length. (C) The ratio of Mzt1 to γTuC is higher at early M phase than during I phase. The ratio of Mzt1 to Alp4^GCP2 levels at SPBs for spindles <3.5 μm in length was measured in GFP-Alp4^GCP2 mCh-Mzt1 cells and compared with that at SPBs during interphase.