Localization of the STB reporter plasmid in meiotic chromosome spreads. (A) Chromosome spreads were prepared from isogenic [cir+] or [cir0] cells (transformed by the STB reporter plasmid) at the leptotene/zygotene or the pachytene stage of meiosis I (3.5 h and 5.5 h after transfer to sporulation medium, respectively). The results were corrected for differences in the percentages of [cir+] and [cir0] cells harboring the reporter plasmid at the time of transfer to sporulation medium. The histograms represent data from ∼200 spreads for t = 3.5 h and ∼800 spreads for t = 5.5 h. In these and subsequent spread assays, the plasmid was detected using an antibody to GFP, which targets the GFP-LacI bound to the LacO array present on the plasmid. (B and C) In the pachytene spreads, chromosomes were visualized by DAPI and the central axes of paired chromosomes by Zip1 (using an antibody to the native protein). Selected sections (boxed regions) of the spreads are enlarged 3× to highlight plasmid foci at chromosome tips. Bars, 2 µm. (D) For the plasmid foci analyzed (>150 for [cir+] spreads; >100 for [cir0] spreads), a plasmid-to-chromosome separation of <0.4 µm was interpreted as colocalization of the two. (E) The chromosome-associated plasmid foci from the [cir+] spreads were distinguished into those at chromosome tips or away from them. The error bars indicate ± SEM. **, P < 0.01 (two-tailed t test).