SC formation depends on SPO11 but SC does not contribute to cohesion in P_CLB2PDS5 cells. (A) SC formation requires Spo11 activity. Yeast cells were induced to undergo synchronous meiosis, and nuclear spreads were prepared for immunofluorescence microscopy as in Fig. 2 A. Zip1 (green) and Rec8-3HA (red) were detected with anti-Zip1 and anti-HA antibodies, respectively. In the absence of Spo11 activity, Zip1 localizes to the polycomplex (PC; arrows). (B) Chromosome morphology in the absence of Zip1. Yeast cells were induced to undergo synchronous meiosis, and nuclear spreads were prepared for immunofluorescence microscopy as in Fig. 2 A. Red, Rec8-3HA; green, Sgo1-9Myc. (C) Sister chromatid cohesion assayed with CEN5-GFP in wild-type (WT), P_CLB2PDS5, zip1Δ, and P_CLB2PDS5 zip1Δ cells. Only one homologue of chromosome V was marked by tetO/tetR-GFP. Yeast cells were induced to undergo synchronous meiosis, aliquots were withdrawn at the indicated times, fixed with 4% formaldehyde, and visualized by fluorescence microscopy. At least 100 cells were counted at each time point.