Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 108, Issue 33, Pages 13671-13676Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1101944108
Keywords
CEN evolution; nucleosome topology; reversome
Categories
Funding
- National Science Foundation [MCB-1049925]
- Robert F. Welch Foundation [F-1274]
- Direct For Biological Sciences
- Div Of Molecular and Cellular Bioscience [1049925] Funding Source: National Science Foundation
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The Saccharomyces cerevisiae 2-mu m plasmid is a multicopy selfish genome that resides in the nucleus. The genetic organization of the plasmid is optimized for stable, high-copy propagation in host-cell populations. The plasmid's partitioning system poaches host factors, including the centromere-specific histone H3-variant Cse4 and the cohesin complex, enabling replicated plasmid copies to segregate equally in a chromosome-coupled fashion. We have characterized the in vivo chromatin topology of the plasmid partitioning locus STB in its Cse4-associated and Cse4-nonassociated states. We find that the occupancy of Cse4 at STB induces positive DNA supercoiling, with a linking difference (Delta Lk) contribution estimated between +1 and +2 units. One plausible explanation for this contrary topology is the presence of a specialized Cse4-containing nucleosome with a right-handed DNA writhe at a functional STB, contrasted by a standard histone H3-containing nucleosome with a left-handed DNA writhe at a nonfunctional STB. The similarities between STB and centromere in their nucleosome signature and DNA topology would be consistent with the potential origin of the unusual point centromere of budding yeast chromosomes from the partitioning locus of an ancestral plasmid.
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