Figure 6.

mps1–737 cells contain two dots of Spc42p-GFP fluorescence, indicating that two SPBs are present. Strains that carry various mps1 alleles and the GFP-tagged allele of SPC42 were shifted to 37°C for 4 h, briefly fixed, and stained with DAPI to visualize DNA. DAPI and GFP fluorescence were then observed. Only large budded cells with evidence of DNA missegregation were scored. The number of dots of GFP fluorescence in a given cell reflects the number of SPBs. (A) At 25°C, large-budded cells display normal DNA segregation patterns (DAPI), and one SPB dot (Spc42p-GFP) localizes with each region of DAPI staining. Shown here are mps1–3796 and mps1–737 strains (AS235-GFP and AS234-GFP, respectively; Table 1). (B) In the mps1–3796 strain at 37°C, aberrant DNA segregation becomes apparent in large-budded cells. Only one SPB dot can be found in most cells, and it is often located close to the bud neck. Similar results were observed for all alleles except mps1–737. (C) When shifted to 37°C, mps1–737 cells behave differently. DNA segregation patterns become aberrant, but most cells clearly contain two distinct SPB dots. Both dots are generally found in the same cell body, and one is often located in a region that does not overlap with DAPI staining (arrow). (D) Number of SPB dots observed in all six mutant backgrounds.