Chromosome length and perinuclear attachment constrain resolution of DNA intertwines.

Abstract

To allow chromosome segregation, topoisomerase II (topo II) must resolve sister chromatid intertwines (SCI) formed during deoxynucleic acid (DNA) replication. How this process extends to the full genome is not well understood. In budding yeast, the unique structure of the ribosomal DNA (rDNA) array is thought to cause late SCI resolution of this genomic region during anaphase. In this paper, we show that chromosome length, and not the presence of rDNA repeats, is the critical feature determining the time of topo II-dependent segregation. Segregation of chromosomes lacking rDNA also requires the function of topo II in anaphase, and increasing chromosome length aggravates missegregation in topo II mutant cells. Furthermore, anaphase Stu2-dependent microtubule dynamics are critical for separation of long chromosomes. Finally, defects caused by topo II or Stu2 impairment depend on attachment of telomeres to the nuclear envelope. We propose that topological constraints imposed by chromosome length and perinuclear attachment determine the amount of SCI that topo II and dynamic microtubules resolve during anaphase.