Precise duplication and segregation of chromosomes is crucial to cellular growth and organismal development. The evolutionary conservation of proteins and protein complexes involved in this process attests to its importance. Cohesin and condensin are two classes of multisubunit complexes required for this critical process. Both human complexes contain a specific heterodimer of SMC (structural maintenance of chromosomes) proteins that constitute the core and additional non-SMC subunits that complete the complex. The condensin complex is a heteropentameric complex that participates in the condensation of chromosomes during cell division by facilitating positive DNA supercoiling and knotting by topoisomerase I and II. There are two condensin complexes which are defined by their non-SMC regulatory subunits. Condensin I is comprised of SMC2, SMC4, CAP-D2, CAP-G, and CAP-H, while condensin II is comprised of SMC2, SMC4, CAP-D3, CAP-G2, and CAP-H2. A basic understanding of the specific roles of some of these subunits has been demonstrated. For example, CAP-D2 may be important for targeting condensin to mitotic chromosomes and metaphase alignment of sister chromatids, CAP-D3 may participate in centromere resolution, and CAPH may have an important role in condensin’s ability to maintain structural integrity of centromeric heterochromatin during mitosis. There is evidence that the condensins also participate in non-mitotic functions such as transcription and replication. Research that further explores the contributions of the subunits of condensin will lead to a better understanding of how condensins and cohesins participate in the maintenance of chromosomes during cell division and their importance to non-mitotic cellular functions.
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