Fig. 3. The continuous presence of cytoplasmic microtubules ensures migration of the ‘old’ SPB into the bud. (A) Transient microtubule depolymerization disrupts SPB inheritance. α-factor-synchronized SPC42–RFP SPC110–GFP cells were incubated with nocodazole to depolymerize microtubules resulting in spindle collapse with two SPBs close together. Nocodazole was then removed by washing. After 1 h samples were analysed for Spc42p–RFP and Spc110p–GFP fluorescence. The indicated percentages are based on three independent experiments (n >80). The arrows point towards the ‘old’ RFP-labelled SPBs. The insets are magnifications of the signals at the top. Abbreviations: D, daughter cell; M, mother cell body. Bar, 5 µm. (B) Interaction of cytoplasmic microtubules with the cell cortex ensures segregation of the ‘old’ SPB into the bud. SPB inheritance was determined in KAR9 SPC42–RFP SPC110–GFP and Δkar9 SPC42–RFP SPC110–GFP cells, after release from α-factor arrest at 30 and 37°C (n = 100; two experiments).