<p><b>a</b>, Schematic of the chromosomal <i>MET3</i>-<i>top2</i><sup>deg</sup> gene encoding thermo-labile Top2<sup>deg</sup> protein and controlled transcriptionally <i>via</i> the presence or absence of methionine in the growth medium. <b>b</b>, Western blot of Top2<sup>deg</sup>. Temperature and carbon-source shifts (<a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003832#pgen.1003832.s002" target="_blank">Figure S2</a>) promote efficient degradation (Tub1-GFP, loading-control). <b>c</b>, Micrographs (left) and quantification (right) of failed nucleus segregation (DAPI) in anaphase cells with elongated spindles (Tub1-GFP) after Top2<sup>deg</sup> was degraded in G1 and the subsequent cell cycle analyzed. Shaded region on graphs indicates the fraction of anaphase nuclei that were not segregated and the top left insets show expanded budding curves. <b>d</b>, CHEF gel analysis of separated chromosomes after Southern blotting to detect catenated topoisomers of the endogenous 2-micron plasmid. Wild type (WT), <i>top2-4</i> and <i>top2<sup>deg</sup></i> strains were initially arrested in G1 (alpha-factor) at 26°C (37°C in the case of <i>top2<sup>deg</sup></i>) or subsequently allowed 2 hours to reach G2/M at 37°C in the presence of nocodazole to prevent anaphase onset (G2/M, 37°C). For <i>top2<sup>deg</sup></i>, additional samples were taken at 45 min and 70 min following alpha factor release at 37°C with nocodazole (Noc. 45 min, Noc. 70 min).</p
