Fig. 4. Deletion of pds5 leads to an increased chromosome segregation failure rate. (A) Rates of mini-chromosome loss were calculated for strains HM248 (pds5⁺) and pds5 Ch16 (pds5) as described in Materials and Methods and are expressed as mean chromosome loss per generation. Arrowheads in the right-hand panels indicate examples of ade^- sectored colonies indicative of chromosome loss. (B) Living GFP-swi6 (pds5⁺) and GFP-swi6 pds5 (pds5) cells were observed by green fluorescence microscopy. In each case a series of three images of a single cell progressing through early anaphase is shown; images were acquired at the time points indicated. (C) Visualisation of lagging chromosomes in pds5 cells. Individual GFP-swi6 pds5 cells were observed as in (B), over a 5 minute period, with images collected every 30 seconds. Bar, 10 µm. (D) Genetic interaction between pds5 and bub1. Ten tetrads derived from a diploid h⁺/h^- pds5:ura4⁺/pds5⁺ bub1::LEU2/bub1⁺ ura4-D18/ura4-DS/E leu1-32/leu1-32 strain were microdissected onto YE agar and the resulting colonies were photographed after 4 days growth at 30°C. The genotypes of the segregants were determined by replica plating and are indicated schematically below (wt, pds5⁺ bub1⁺; p, pds5:ura4⁺; b, bub1::LEU2; pb, pds5:ura4⁺ bub1::LEU2; the latter is also indicated by white boxes in the upper panel). The inset panel shows a micrograph of a representative pds5:ura4⁺ bub1::LEU2 colony taken at the same time. Bar, 20 µm. (E) Slow growth of pds5 bub1 cells is associated with chromosome segregation defects. Fluorescence micrographs of formaldehyde fixed, DAPI-stained cells from exponentially growing YE liquid cultures of HM123 (pds5⁺) and the indicated strains. Cells exhibiting abnormal chromosome segregation are indicated (arrowheads).