1. Condensin-Based Chromosome Organization from Bacteria to Vertebrates
Tatsuya Hirano 
Cell 
Volume 164, Issue 5, Pages (February 2016)
DOI: /j.cell
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2. Figure 1 Architecture and Action of Condensin Complexes
(A) Subunit composition. The eukaryotic condensin complexes (condensin I and condensin II) share the same heterodimeric pair of SMC subunits (SMC2 and SMC4). They have distinct sets of non-SMC regulatory subunits, each set composed of a kleisin subunit (CAP-H and -H2) and a pair of HEAT subunits (CAP-D2/G and CAP-D3/G2). SMC-ScpAB is a bacterial condensin from B. subtilis, which is composed of an SMC homodimer, a kleisin subunit (ScpA), and an ScpB dimer.
(B) Assembly of eukaryotic condensin I. The SMC dimer adopts a V-shaped molecule with two coiled-coil arms. The hinge domain is responsible for dimerization, and ATP-binding head domains are located at distal ends of the arms. The kleisin subunit is predicted to bridge the two head domains through an asymmetric binding mode. The two HEAT subunits associate with the central region of the kleisin subunit to form a holocomplex.
(C) The SMC ATPase cycle. Engagement and disengagement of the two head domains regulated by ATP binding and hydrolysis are depicted.
(D) A postulated scheme for DNA entrapment. Initial DNA binding of condensins could occur at the SMC hinge domain. ATP binding would induce head-head engagement, which in turn disrupts an SMC-kleisin interface. ATP hydrolysis then triggers head-head disengagement, thereby opening the otherwise closed ring structure. Re-closing of the ring leads to entrapment of the DNA strand.
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3. Figure 2
Models of Chromosome Assembly and Segregation in Eukaryotes and Bacteria
(A) Chromosome assembly and resolution in vertebrates. In this admittedly oversimplified model, the division of labor of the two condensin complexes is emphasized although their functions are partially overlapped with each other. It is also important to bear in mind that chromosome axes depicted here are by no means a static structure (see the text for details).
(B) Chromosome segregation in B. subtilis. Chromosome replication and segregation occur simultaneously in bacterial cells. A population of SMC (dark magenta) is recruited to the parS sites proximal to origins (yellow circles) and helps their segregation by forming SMC foci (or the condensation center). Another more mobile population of SMC (light magenta) functions along whole regions of chromosomes and contributes to their segregation.
(C) Anaphase chromosome segregation in C. merolae. Upon entry into mitosis, condensin II accumulates at clustered centromeres and participates in their resolution by metaphase. Condensin I associates broadly with arms by metaphase and promotes their segregation in anaphase.
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4. Figure 3
Evolution of Condensin Complexes and Their Physiological Functions
It is most likely that the last universal common ancestor (LUCA) had an ancestral form of condensins that helped segregate duplicated chromosomes. Then the cell nucleus was invented to create eukaryotes (“eukaryogenesis”). It is reasonable to predict that the last eukaryotic common ancestor (LECA) had ancestral forms of both condensins I and II. Among the currently existing organisms, chromosomes of C. merolae might retain many properties of those of LECA (path #1). See the text for the three possible paths of eukaryotic chromosome evolution depicted here (paths #2–4). The genome size (Mb) of each organism is shown in red.
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5. Figure 4 Interphase Chromosome Organization by Condensins
(A) Condensin II contributes to unpairing of homologous chromosomes in somatic diploid cells in D. melanogaster.
(B) Condensin II contributes to the formation of chromosome territories in polyploid nurse cells in D. melanogaster.
(C) Condensin II prevents hyperclustering of chromocenters in neuronal stem cells (NSCs) in mice.
(D) A condensin I-like complex (condensin IDCC) regulates dosage compensation by altering the conformation of the X chromosome in C. elegans hermaphrodites.
Cell  , DOI: ( /j.cell )
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