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Originally published In Press as doi:10.1074/jbc.M307025200 on August 6, 2003
J. Biol. Chem., Vol. 278, Issue 43, 41607-41617, October 24, 2003
Plasmid Accumulation Reduces Life Span in Saccharomyces cerevisiae*
Alaric A. Falcón and
John P. Aris
From the
Department of Anatomy and Cell Biology, University of Florida, Gainesville, Florida 32610-0235
Aging in the yeast Saccharomyces cerevisiae is under the control of multiple pathways. The production and accumulation of extrachromosomal rDNA circles (ERCs) is one pathway that has been proposed to bring about aging in yeast. To test this proposal, we have developed a plasmid-based model system to study the role of DNA episomes in reduction of yeast life span. Recombinant plasmids containing different replication origins, cis-acting partitioning elements, and selectable marker genes were constructed and analyzed for their effects on yeast replicative life span. Plasmids containing the ARS1 replication origin reduce life span to the greatest extent of the plasmids analyzed. This reduction in life span is partially suppressed by a CEN4 centromeric element on ARS1 plasmids. Plasmids containing a replication origin from the endogenous yeast 2 µ circle also reduce life span, but to a lesser extent than ARS1 plasmids. Consistent with this, ARS1 and 2 µ origin plasmids accumulate in 7-generation-old cells, but ARS1/CEN4 plasmids do not. Importantly, ARS1 plasmids accumulate to higher levels in old cells than 2 µ origin plasmids, suggesting a correlation between plasmid accumulation and life span reduction. Reduction in life span is neither an indirect effect of increased ERC levels nor the result of stochastic cessation of growth. The presence of a fully functional 9.1-kb rDNA repeat on plasmids is not required for, and does not augment, reduction in life span. These findings support the view that accumulation of DNA episomes, including episomes such as ERCs, cause cell senescence in yeast.
Received for publication, July 1, 2003
, and in revised form, August 5, 2003.
* This project was supported in part by funding from the Ellison Medical Foundation. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
To whom correspondence should be addressed. Tel.: 352-392-1873; Fax: 352-392-3305; E-mail: johnaris{at}ufl.edu.

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Copyright © 2003 by the American Society for Biochemistry and Molecular Biology.
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