Partitioning of the 2-microm circle plasmid of Saccharomyces cerevisiae. Functional coordination with chromosome segregation and plasmid-encoded rep protein distribution.
The efficient partitioning of the 2-microm plasmid of Saccharomyces cerevisiae at cell division is dependent on two plasmid-encoded proteins (Rep1p and Rep2p), together with the cis-acting locus REP3 (STB). In addition, host encoded factors are likely to contribute to plasmid segregation. Direct observation of a 2-microm-derived plasmid in live yeast cells indicates that the multiple plasmid copies are located in the nucleus, predominantly in clusters with characteristic shapes. Comparison to a single-tagged chromosome or to a yeast centromeric plasmid shows that the segregation kinetics of the 2-microm plasmid and the chromosome are quite similar during the yeast cell cycle. Immunofluorescence analysis reveals that the plasmid is colocalized with the Rep1 and Rep2 proteins within the yeast nucleus. Furthermore, the Rep proteins (and therefore the plasmid) tend to concentrate near the poles of the yeast mitotic spindle. Depolymerization of the spindle results in partial dispersion of the Rep proteins in the nucleus concomitant with a loosening in the association between plasmid molecules. In an ipl1-2 yeast strain, shifted to the nonpermissive temperature, the chromosomes and plasmid almost always missegregate in tandem. Our results suggest that, after DNA replication, plasmid distribution to the daughter cells occurs in the form of specific DNA-protein aggregates. They further indicate that the plasmid partitioning mechanism may exploit at least some of the components of the cellular machinery required for chromosomal segregation.
Velmurugan
S
S
Section of Molecular Genetics and Microbiology, Institute for Cell and Molecular Biology, University of Texas at Austin, Austin, Texas 78712, USA.
Yang
X M
XM
Chan
C S
CS
Dobson
M
M
Jayaram
M
M
D002453:Cell Cycle; D002455:Cell Division; D020090:Chromosome Segregation; D002875:Chromosomes / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D005656:Fungal Proteins / Q000378:metabolism; D008870:Microtubules / Q000378:metabolism; D009154:Mutation; D015739:Nocodazole / Q000494:pharmacology; D009687:Nuclear Proteins / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism*; D011498:Protein Precursors / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D008941:Spindle Apparatus / Q000378:metabolism; D015534:Trans-Activators / Q000378:metabolism
D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D009687:Nuclear Proteins; D011498:Protein Precursors; C491137:REP1 protein, S cerevisiae; C490689:REP2 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators; D015739:Nocodazole