Condensin and cohesin complexity: the expanding repertoire of functions

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Abstract
Cohesin contributes to intrachromosomal loops that regulate metazoan gene expression by constraining interactions between promoter and enhancer elements. These structures can be subject to regulation during development. Condensin binds yeast tRNA genes to promote their aggregation at the nucleolus and can inhibit interactions between homologous chromosomes during interphase. The Caenorhabditis elegans dosage compensation complex serves as a paradigm for the regulation of gene expression by condensin. The complex regulates transcription across an entire sex chromosome but does not always bind in proximity to regulatory targets. Cohesin is required for the acquisition of cell-lineage-specific traits in the Drosophila melanogaster nervous system, and this role does not require passage through the cell cycle. Meiosis-specific functions of condensin and cohesin abound. Condensin regulates the number and distribution of double-strand breaks and crossovers, whereas cohesin is essential for the assembly of a structure called the axial element, which forms on meiotic chromosomes and is important for proper association of homologous chromosomes and for crossover recombination. Specialization of condensin and cohesin function is achieved through swapping of homologous subunits to create molecular machines with similar architecture but distinct biological roles.