Nutrient starvation promotes condensin loading to maintain rDNA stability.

Nutrient starvation or rapamycin treatment, through inhibition of target of rapamycin, causes condensation of ribosomal DNA (rDNA) array and nucleolar contraction in budding yeast. Here we report that under such conditions, condensin is rapidly relocated into the nucleolus and loaded to rDNA tandem repeats, which is required for rDNA condensation. Rpd3-dependent histone deacetylation is necessary and sufficient for condensin's relocalization and loading to rDNA array, suggesting that histone modification plays a regulatory role for condensin targeting. Rapamycin independently, yet coordinately, inhibits rDNA transcription and promotes condensin loading to rDNA array. Unexpectedly, we found that inhibition of rDNA transcription in the absence of condensin loading leads to rDNA instability. Our data suggest that enrichment of condensin prevents rDNA instability during nutrient starvation. Together, these observations unravel a novel role for condensin in the maintenance of regional genomic stability.