2 micron plasmid hitchhikes on mitotic mechanism of Saccharomyces cerevisiae to maintain equal distribution in host

Published online April 13, 2009
doi:10.1083/jcb.200810130
The Journal of Cell Biology, Vol. 185, No. 2, 251-264
The Rockefeller University Press, 0021-9525 $30.00
© 2009 Cui et al.

The selfish yeast plasmid uses the nuclear motor Kip1p but not Cin8p for its localization and equal segregation

Hong Cui, Santanu K. Ghosh, and Makkuni Jayaram
Section of Molecular Genetics and Microbiology, University of Texas at Austin, Austin, TX 78712

Correspondence to Makkuni Jayaram: jayaram@icmb.utexas.edu


The 2 micron plasmid of Saccharomyces cerevisiae uses the Kip1 motor, but not the functionally redundant Cin8 motor, for its precise nuclear localization and equal segregation. The timing and lifetime of Kip1p association with the plasmid partitioning locus STB are consistent with Kip1p being an authentic component of the plasmid partitioning complex. Kip1–STB association is not blocked by disassembling the mitotic spindle. Lack of Kip1p disrupts recruitment of the cohesin complex at STB and cohesion of replicated plasmid molecules. Colocalization of a 2 micron reporter plasmid with Kip1p in close proximity to the spindle pole body is reminiscent of that of a CEN reporter plasmid. Absence of Kip1p displaces the plasmid from this nuclear address, where it has the potential to tether to a chromosome or poach chromosome segregation factors. Exploiting Kip1p, which is subsidiary to Cin8p for chromosome segregation, to direct itself to a "partitioning center" represents yet another facet of the benign parasitism of the yeast plasmid.