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Mol Cell. 2018 Nov 1;72(3):583-593.e4. doi: 10.1016/j.molcel.2018.08.036. Epub 2018 Oct 4.

Genomic Copy-Number Loss Is Rescued by Self-Limiting Production of DNA Circles.

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Department of Biology, New York University, New York, NY 10003, USA.
Biology Department, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, NY 10016, USA.
Department of Biology, New York University, New York, NY 10003, USA. Electronic address:


Copy-number changes generate phenotypic variability in health and disease. Whether organisms protect against copy-number changes is largely unknown. Here, we show that Saccharomyces cerevisiae monitors the copy number of its ribosomal DNA (rDNA) and rapidly responds to copy-number loss with the clonal amplification of extrachromosomal rDNA circles (ERCs) from chromosomal repeats. ERC formation is replicative, separable from repeat loss, and reaches a dynamic steady state that responds to the addition of exogenous rDNA copies. ERC levels are also modulated by RNAPI activity and diet, suggesting that rDNA copy number is calibrated against the cellular demand for rRNA. Last, we show that ERCs reinsert into the genome in a dosage-dependent manner, indicating that they provide a reservoir for ultimately increasing rDNA array length. Our results reveal a DNA-based mechanism for rapidly restoring copy number in response to catastrophic gene loss that shares fundamental features with unscheduled copy-number amplifications in cancer cells.


Fob1; Hmo1; copy-number variations; eccDNA; genome instability; rDNA; rRNA genes

[Available on 2019-11-01]
[Indexed for MEDLINE]

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