Live-cell imaging reveals a stable cohesin-chromatin interaction after but not before DNA replication

Curr Biol. 2006 Aug 8;16(15):1571-8. doi: 10.1016/j.cub.2006.06.068.

Abstract

Cohesin is a multisubunit protein complex that links sister chromatids from replication until segregation. The lack of obvious cohesin-targeting-specific sequences on DNA, as well as cohesin's molecular arrangement as a large ring, has led to the working hypothesis that cohesin acts as a direct topological linker. To preserve the identity of sister chromatids, such a linkage would need to stably persist throughout the entire S and G2 phases of the cell cycle. Unexpectedly, cohesin binds chromatin already in telophase, and a large fraction dissociates from chromosomes during prophase in a phosphorylation-dependent manner, whereas initiation of anaphase requires proteolytic cleavage of only a small fraction of cohesin. These observations raised the question of how and when cohesin interacts with chromatin during the cell cycle. Here, we report a cell-cycle dependence in the stability of cohesin binding to chromatin. Using photobleaching and quantitative live-cell imaging, we identified several cohesin pools with different chromatin binding stabilities. Although all chromatin bound cohesin dissociated after a mean residence time of less than 25 min before replication, about one-third of cohesin was bound much more stably after S phase and persisted until metaphase, consistent with long-lived links mediating cohesion between sister chromatids.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Cycle / physiology*
  • Cell Cycle Proteins / metabolism*
  • Cell Line
  • Chromatin / metabolism*
  • Chromosomal Proteins, Non-Histone / metabolism*
  • DNA Replication / physiology*
  • Fluorescence Recovery After Photobleaching
  • Humans
  • Microscopy, Fluorescence
  • Models, Biological
  • Nuclear Proteins / metabolism*

Substances

  • Cell Cycle Proteins
  • Chromatin
  • Chromosomal Proteins, Non-Histone
  • Nuclear Proteins
  • cohesins