Microtubule‐associated proteins, B ik1 and B im1, are required for faithful partitioning of the endogenous 2 micron plasmids in budding yeast

• Published in: Molecular microbiology Vol. 103; no. 6; pp. 1046 - 1064
• Main Authors: Prajapati, Hemant Kumar, Rizvi, Syed Meraj Azhar, Rathore, Ishan, Ghosh, Santanu K.
• Format: Journal Article
• Language: English
• Published: 01-03-2017
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1111/mmi.13608

Summary
The 2 μ plasmid of budding yeast shows high mitotic stability similar to that of chromosomes by using its self‐encoded systems, namely partitioning and amplification. The partitioning system consists of the plasmid‐borne proteins Rep1, Rep2 and a
cis
‐acting locus
STB
that, along with several host factors, ensures efficient segregation of the plasmid. The plasmids show high stability as they presumably co‐segregate with chromosomes through utilization of various host factors. To acquire these host factors, the plasmids are thought to localize to a certain sub‐nuclear locale probably assisted by the motor protein, Kip1 and microtubules. Here, we show that the microtubule‐associated proteins Bik1 and Bim1 are also important host factors in this process, perhaps by acting as an adapter between the plasmid and the motor and thus helping to anchor the plasmid to microtubules. Abrogation of Kip1 recruitment at
STB
in the absence of Bik1 argues for its function at
STB
upstream of Kip1. Consistent with this, both Bik1 and Bim1 associate with plasmids without any assistance from the Rep proteins. As observed earlier with other host factors, lack of Bik1 or Bim1 also causes a cohesion defect between sister plasmids leading to plasmid missegregation.