SC formation during meiosis. (A) Immunofluorescence analysis of SC formation in wild-type (WT) and P_CLB2PDS5 cells. 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. Note that Zip1 still localizes to chromosomes in P_CLB2PDS5 cells despite the absence of homologue synapsis. (B, left) EM of SC formation in wild-type and P_CLB2PDS5 cells. Yeast nuclear spreads were stained with silver nitrate and visualized by EM. (middle) Magnified views of boxed regions are shown. (top right) A twofold enlargement of regions of interest is shown. (bottom right) Diagrams of sister chromatids are shown in black and gray. Note that short stretches of LEs are formed in P_CLB2PDS5 cells despite the absence of homologue synapsis. (C) Distribution of chromosome axial length from wild type (black bars) and P_CLB2PDS5 (gray bars). Eight cells from each stain were scored. (D) Immunofluorescence analysis of SC formation in haploid yeast cells. Haploids were induced to undergo synchronous meiosis for 8 h and processed as described in A. These haploid strains could enter meiosis because the SIR2 gene had been deleted, resulting in activation of both mating types. Rec8-3HA (red) and Zip1 (green) were detected as described in A. The arrow shows the polycomplex formed by aggregation of SC components.