Figure 2.

Analysis of rDNA array stability and condensation. (A) Suppression of synthetic lethality by deletion of the rDNA array. ycs4-2::NAT RDN1 (YBL624) and rdn1Δ (YBL625) strains were crossed with indicated nucleolar gene deletions (xxxΔ::KAN in MN70; YBL562-1, YBL563-1, YBL564-1, and YBL568-1). In rdn1Δ strains, the rDNA was carried on a high copy plasmid. After dissection of meiotic progeny, double mutant combinations (circled) were identified or inferred using drug markers. (B) Deletion of the rDNA array did not suppress the temperature sensitivity of ycs4-2::NAT. Fivefold dilutions of indicated strains (W303, MN70, YBL624, and YBL625) were spotted on rich media and incubated at the indicated temperature for 2–3 d. (C and D) Fluorescence in situ hybridization of the yeast RDN locus. Deletion mutants in WT (YPH499) or cdc15-1 (YBL304-1) backgrounds as indicated were arrested in metaphase (nocodazole, 23°C, C) or anaphase (cdc15-1 mutation, 37°C, D) and processed for rDNA FISH (see Materials and Methods). Micrographs show the rDNA signal in green with the bulk chromosomes in red. In WT cells, condensed rDNA adopts a distinct loop (metaphase) or line (anaphase) morphology, whereas decondensed rDNA appears as a disorganized puff. Quantitation of the rDNA condensation in metaphase or anaphase arrested cells, respectively. Numbers reflect the percent nuclei with condensed rDNA loops (C) or lines (D). At least 100 nuclei were score per sample.