title: A novel role for the mitotic spindle during DNA segregation in yeast: promoting 2 microm plasmid-cohesin association.
abstract: The 2 microm circle plasmid in Saccharomyces cerevisiae is a model for a stable, high-copy-number, extrachromosomal "selfish" DNA element. By combining a partitioning system and an amplification system, the plasmid ensures its stable propagation and copy number maintenance, even though it does not provide any selective advantage to its host. Recent evidence suggests that the partitioning system couples plasmid segregation to chromosome segregation. We now demonstrate an unexpected and unconventional role for the mitotic spindle in the plasmid-partitioning pathway. The spindle specifies the nuclear address of the 2 microm circle and promotes recruitment of the cohesin complex to the plasmid-partitioning locus STB. Only the nuclear microtubules, and not the cytoplasmic ones, are required for loading cohesin at STB. In cells recovering from nocodazole-induced spindle depolymerization and G(2)/M arrest, cohesin-STB association can be established coincident with spindle restoration. This postreplication recruitment of cohesin is not functional in equipartitioning. However, normally acquired cohesin can be inactivated after replication without causing plasmid missegregation. In the mtw1-1 mutant yeast strain, the plasmid cosegregates with the spindle and the spindle-associated chromosomes; by contrast, a substantial number of the chromosomes are not associated with the spindle. These results are consistent with a model in which the spindle promotes plasmid segregation in a chromosome-linked fashion.
authors.affiliation: Section of Molecular Genetics and Microbiology, University of Texas at Austin, Austin, TX 78712, USA.
authors.forename: Shwetal
authors.initials: S
authors.lastname: Mehta
authors.forename: Xian-Mei
authors.initials: XM
authors.lastname: Yang
authors.forename: Makkuni
authors.initials: M
authors.lastname: Jayaram
authors.forename: Soundarapandian
authors.initials: S
authors.lastname: Velmurugan
mesh_terms: D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D002868:Chromosomal Proteins, Non-Histone; D020090:Chromosome Segregation / Q000187:drug effects / Q000502:physiology*; D015825:Chromosomes, Fungal / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D005656:Fungal Proteins / Q000378:metabolism; D018386:Kinetochores; D008870:Microtubules / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D015739:Nocodazole / Q000494:pharmacology; D009687:Nuclear Proteins / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism; D010957:Plasmids / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D008941:Spindle Apparatus / Q000502:physiology*; D015534:Trans-Activators / Q000378:metabolism; D014404:Tubulin / Q000235:genetics; D000097722:Cohesins
chemical_list: D018797:Cell Cycle Proteins; D002868:Chromosomal Proteins, Non-Histone; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D015739:Nocodazole; D009687:Nuclear Proteins; D010750:Phosphoproteins; D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators; D014404:Tubulin; D000097722:Cohesins; C490529:MCD1 protein, S cerevisiae; C120362:MTW1 protein, S cerevisiae; C051237:REP protein, yeast plasmid; C490689:REP2 protein, S cerevisiae