title: The partitioning and copy number control systems of the selfish yeast plasmid: an optimized molecular design for stable persistence in host cells.
abstract: The multi-copy 2 micron plasmid of Saccharomyces cerevisiae, a resident of the nucleus, is remarkable for its high chromosome-like stability. The plasmid does not appear to contribute to the fitness of the host, nor does it impose a significant metabolic burden on the host at its steady state copy number. The plasmid may be viewed as a highly optimized selfish DNA element whose genome design is devoted entirely towards efficient replication, equal segregation and copy number maintenance. A partitioning system comprised of two plasmid coded proteins, Rep1 and Rep2, and a partitioning locus STB is responsible for equal or nearly equal segregation of plasmid molecules to mother and daughter cells. Current evidence supports a model in which the Rep-STB system promotes the physical association of the plasmid with chromosomes and thus plasmid segregation by a hitchhiking mechanism. The Flp site-specific recombination system housed by the plasmid plays a critical role in maintaining steady state plasmid copy number. A decrease in plasmid population due to rare missegregation events is rectified by plasmid amplification via a recombination induced rolling circle replication mechanism. Appropriate plasmid amplification, without runaway increase in copy number, is ensured by positive and negative regulation of FLP gene expression by plasmid coded proteins and by the control of Flp level/activity through host mediated post-translational modification(s) of Flp. The Flp system has been successfully utilized to understand mechanisms of site-specific recombination, to bring about directed genetic alterations for addressing fundamental problems in biology, and as a tool in biotechnological applications.
authors.affiliation: Section of Molecular Genetics and Microbiology, Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas 78712.
authors.forename: Yen-Ting
authors.initials: YT
authors.lastname: Liu
authors.affiliation: Section of Molecular Genetics and Microbiology, Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas 78712.
authors.forename: Saumitra
authors.initials: S
authors.lastname: Sau
authors.affiliation: Section of Molecular Genetics and Microbiology, Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas 78712.
authors.forename: Chien-Hui
authors.initials: CH
authors.lastname: Ma
authors.affiliation: Section of Molecular Genetics and Microbiology, Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas 78712.
authors.forename: Aashiq H
authors.initials: AH
authors.lastname: Kachroo
authors.affiliation: Section of Molecular Genetics and Microbiology, Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas 78712.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Rowley
authors.affiliation: Section of Molecular Genetics and Microbiology, Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas 78712.
authors.forename: Keng-Ming
authors.initials: KM
authors.lastname: Chang
authors.affiliation: Department of Life Sciences and Institute of Genome Sciences, National Yang-Ming University, Taipei 112, Taiwan.
authors.forename: Hsiu-Fang
authors.initials: HF
authors.lastname: Fan
authors.affiliation: Department of Life Sciences and Institute of Genome Sciences, National Yang-Ming University, Taipei 112, Taiwan.
authors.forename: Makkuni
authors.initials: M
authors.lastname: Jayaram
mesh_terms: D002455:Cell Division; D004261:DNA Replication; D004271:DNA, Fungal / Q000235:genetics* / Q000378:metabolism*; D005800:Genes, Fungal; D042822:Genomic Instability; D010957:Plasmids; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D004271:DNA, Fungal; D029701:Saccharomyces cerevisiae Proteins