Condensin action and compaction

Abstract

Condensin is a multi-subunit protein complex that belongs to the family of structural maintenance of chromosomes (SMC) complexes. Condensins regulate chromosome structure in a wide range of processes including chromosome segregation, gene regulation, DNA repair and recombination. Recent research defined the structural features and molecular activities of condensins, but it is unclear how these activities are connected to the multitude of phenotypes and functions attributed to condensins. In this review, we briefly discuss the different molecular mechanisms by which condensins may regulate global chromosome compaction, organization of topologically associated domains, clustering of specific loci such as tRNA genes, rDNA segregation, and gene regulation.

Keywords: Chromosome interactions; Chromosome segregation; Clustering; Condensin; Genome organization; SMC complexes; TADs; Transcription; gene expression; rDNA; tRNA.

Figure 1. Condensin-mediated genome organization:

(A) Mitotic structure of chromosomes in yeast (Ai) and metazoans (Aii). (Ai) In yeast, condensin compacts the rDNA and tethers the rDNA to the centromere. The centromere-proximal side of the rDNA is enriched for condensin, which compacts chromosomes through loop extrusion. (Aii) In metazoans there are two condensin complexes, which function on different scales (condensin I: shorter loops, condensin II: longer loops). Together, condensin I and II compact chromosomes through loop extrusion, forming nested loop structures. (B) Interphase structure of chromosomes in yeast (Bi) and metazoans (Bii). (Bi) In yeast, condensin compacts chromosomes through loop extrusion and aids clustering of tRNAs and transposons by promoting long-range interactions. (Bii) In metazoans, condensin compacts chromosomes through loop extrusion, clusters transposons and enhancer-promoter pairs by promoting long-range interactions, and aids the formation of TADs.