Ghosh Santanu K, Hajra Sujata, Jayaram Makkuni
Section of Molecular Genetics and Microbiology, University of Texas, Austin, TX 78712, USA.
Proc Natl Acad Sci U S A. 2007 Aug 7;104(32):13034-9. doi: 10.1073/pnas.0702996104. Epub 2007 Aug 1.
The 2-microm yeast plasmid, a benign high-copy nuclear parasite, propagates itself with nearly the same fidelity as the chromosomes of its host. Equal plasmid segregation is absolutely dependent on the cohesin complex assembled at the plasmid partitioning locus STB. However, the mechanism of cohesin action in the context of multiple plasmid copies, resident within two separate clusters after DNA replication, is unknown. By using "single-copy" derivatives of the 2-microm plasmid, we demonstrate that recruitment of cohesin at STB during S phase indeed translates into cohesion between plasmid molecules. Through binary fluorescence tagging, we reveal that segregation of replicated plasmids occurs in a sister-to-sister fashion. Thus, cohesin serves the same fundamental purpose in plasmid and chromosome segregation.
2 微米酵母质粒是一种良性高拷贝核寄生体，其自身繁殖的保真度几乎与宿主染色体相同。质粒的均等分离绝对依赖于在质粒分配位点 STB 组装的黏连蛋白复合体。然而，在 DNA 复制后位于两个独立簇中的多个质粒拷贝情况下，黏连蛋白的作用机制尚不清楚。通过使用 2 微米质粒的“单拷贝”衍生物，我们证明在 S 期 STB 处募集黏连蛋白确实会转化为质粒分子之间的黏连。通过二元荧光标记，我们发现复制后的质粒以姐妹对姐妹的方式进行分离。因此，黏连蛋白在质粒和染色体分离中起着相同的基本作用。
