Completion of Chr XII duplication is specifically delayed in orc2-1 cells but restored by reduction of the rDNA copy numbers. (A) The status of Chr XII and Chr II in exponentially growing NOY408-1b (ORC2 FOB1 RDN150), YNV1 (orc2-1 FOB1 RDN150), NOY408-1bf30 (ORC2 fob1Δ rdnΔ30), and YNV15 (orc2-1 fob1Δ rdnΔ30) was examined by PFGE as described in Materials and Methods. Each strain was incubated in YPD at 26°C for 6 h after the temperature shift from 23°C. Cells were collected and prepared in agarose plugs for PFGE. Chromosome patterns were detected and quantified by Southern hybridization using Chr XII- and Chr II-specific probes, as described in Materials and Methods. (B) The percentages of chromosomes which remained in the plug after electrophoresis (XII* and II*) were quantified for NOY408-1b (ORC2 FOB1 RDN150), YNV1 (orc2-1 FOB1 RDN150), NOY408-1bf30 (ORC2 fob1Δ rdnΔ30), and YNV15 (orc2-1 fob1Δ rdnΔ30) grown at 23°C and 26°C for 6 h. Average values from three independent experiments are shown. Error bars represent standard deviations.