Condensins are large protein complex

Protein complex

A multiprotein complex is a group of two or more associated polypeptide chains. If the different polypeptide chains contain different protein domain, the resulting multiprotein complex can have multiple catalytic functions...

es that play a central role in chromosome

Chromosome

A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...

 assembly and segregation in eukaryotic cells.

Subunit composition

Many eukaryotic cells possess two different types of condensin complexes, known as condensin I and condensin II. The two complexes share the same pair of core subunits, SMC2 and SMC4, both belonging to a large family of chromosomal ATPases, known as SMC proteins. SMC stands for Structural Maintenance of Chromosomes. Each of the complexes contains a distinct set of non-SMC regulatory subunits. The nematode Caenorhabditis elegans

Caenorhabditis elegans

Caenorhabditis elegans is a free-living, transparent nematode , about 1 mm in length, which lives in temperate soil environments. Research into the molecular and developmental biology of C. elegans was begun in 1974 by Sydney Brenner and it has since been used extensively as a model...

 has a condensin I-related complex involved in dosage compensation (DCC).

Complex	Subunit	Classification	S. cerevisiae	S. pombe	C. elegans	D. melanogaster	Vertebrates (human genes)
condensin I & II	SMC2	ATPase	Smc2	Cut14	MIX-1	DmSmc2	CAP-E (SMC2 SMC2 Structural maintenance of chromosomes protein 2 also known as chromosome-associated protein E is a protein that in humans is encoded by the SMC2 gene.... )
condensin I & II	SMC4	ATPase	Smc4	Cut3	SMC-4	DmSmc4	CAP-C (SMC4 SMC4 Structural maintenance of chromosomes protein 4 also known as chromosome-associated polypeptide C or XCAP-C homolog is a protein that in humans is encoded by the SMC4 gene. SMC-4 is a core subunit of condensin I and II, large protein complexes involved in chromosome condensation... )
condensin I	CAP-D2	HEAT	Ycs4	Cnd1	DPY-28	CG1911	CAP-D2 (NCAPD2 NCAPD2 Condensin complex subunit 1 also known as chromosome-associated protein D2 or non-SMC condensin I complex subunit D2 or XCAP-D2 homolog is a protein that in humans is encoded by the NCAPD2 gene. CAP-D2 is a subunit of condensin I, a large protein complex involved in chromosome condensation.... )
condensin I	CAP-G	HEAT	Ycg1	Cnd3	CAP-G1	cap-g	CAP-G (NCAPG NCAPG Condensin complex subunit 3 also known as condensin subunit CAP-G or non-SMC condensin I complex subunit G is a protein that in humans is encoded by the NCAPG gene. CAP-G is a subunit of condensin I, a large protein complex involved in chromosome condensation.... )
condensin I	CAP-H	kleisin	Brn1	Cnd2	DPY-26	barren	CAP-H (NCAPH NCAPH Condensin complex subunit 2 also known as chromosome-associated protein H or non-SMC condensin I complex subunit H is a protein that in humans is encoded by the NCAPH gene... )
condensin II	CAP-D3	HEAT	-	-	HCP-6	CG31989	CAP-D3 (NCAPD3 NCAPD3 Condensin-2 complex subunit D3 also known as non-SMC condensin II complex subunit D3 is a protein that in humans is encoded by the NCAPD3 gene. CAP-D3 is a subunit of condensin II, a large protein complex involved in chromosome condensation... )
condensin II	CAP-G2	HEAT	-	-	CAP-G2	-?	CAP-G2 (NCAPG2 NCAPG2 Condensin-2 complex subunit G2 also known as chromosome-associated protein G2 or leucine zipper protein 5 is a protein that in humans is encoded by the NCAPG2 gene. CAP-G2 is a subunit of condensin II, a large protein complex involved in chromosome condensation.... )
condensin II	CAP-H2	kleisin	-	-	KLE-2	CG14685	CAP-H2 (NCAPH2 NCAPH2 Condensin-2 complex subunit H2, also known as chromosome-associated protein H2 or non-SMC condensin II complex subunit H2 , is a protein that in humans is encoded by the NCAPH2 gene. CAP-H2 is a subunit of condensin II, a large protein complex involved in chromosome condensation.... )
condensin I (DCC)	SMC4 variant	ATPase	-	-	DPY-27	-	-

Evolution

The structure and function of condensin I are conserved from yeast to humans, but yeast has no condensin II. The nematode Caenorhabditis elegans possesses both condensin I and II, yet has a third complex (closely related to condensin I) that participates in chromosome-wide gene regulation, i.e., dosage compensation

Dosage compensation

Dosage compensation, also known as Ohno's Hypothesis, is a hypothetical genetic regulatory mechanism which operates to equalize the phenotypic expression of characteristics determined by genes on the X chromosome so that they are equally expressed in the human XY male and the XX female. In 2006,...

. Even in bacterial cells, ancestral forms of condensins regulate the organization and segregation of their chromosomes (nucleoids).

Subcellular localization and regulation

In human tissue culture cells, the two condensin complexes are regulated differently during the cell cycle

Cell cycle

The cell cycle, or cell-division cycle, is the series of events that takes place in a cell leading to its division and duplication . In cells without a nucleus , the cell cycle occurs via a process termed binary fission...

. Condensin II is present within the cell nucleus

Cell nucleus

In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...

 during interphase

Interphase

Interphase is the phase of the cell cycle in which the cell spends the majority of its time and performs the majority of its purposes including preparation for cell division. In preparation for cell division, it increases its size and makes a copy of its DNA...

 and is involved in an early stage of chromosome condensation within the prophase

Prophase

Prophase, from the ancient Greek πρό and φάσις , is a stage of mitosis in which the chromatin condenses into a highly ordered structure called a chromosome in which the chromatin becomes visible. This process, called chromatin condensation, is mediated by the condensin complex...

 nucleus. On the other hand, condensin I is present in the cytoplasm

Cytoplasm

The cytoplasm is a small gel-like substance residing between the cell membrane holding all the cell's internal sub-structures , except for the nucleus. All the contents of the cells of prokaryote organisms are contained within the cytoplasm...

 during interphase, and gains access to chromosomes only after the nuclear envelope

Nuclear envelope

A nuclear envelope is a double lipid bilayer that encloses the genetic material in eukaryotic cells. The nuclear envelope also serves as the physical barrier, separating the contents of the nucleus from the cytosol...

 breaks down at the end of prophase. During prometaphase

Prometaphase

Prometaphase is the phase of mitosis following prophase and preceding metaphase, in eukaryotic somatic cells. In Prometaphase, The nuclear envelope breaks into fragments and disappears. The tiny nucleolus inside the nuclear envolope, also dissolves. Microtubules emerging from the centrosomes at the...

 and metaphase

Metaphase

Metaphase, from the ancient Greek μετά and φάσις , is a stage of mitosis in the eukaryotic cell cycle in which condensed & highly coiled chromosomes, carrying genetic information, align in the middle of the cell before being separated into each of the two daughter cells...

, both condensin I and condensin II contribute to the assembly of condensed chromosomes, in which two sister chromatids

Sister chromatids

Sister chromatids are two identical copies of a chromatid connected by a centromere. Compare sister chromatids to homologous chromosomes, which are the two different copies of the same chromosome that diploid organisms inherit, one from each parent...

 are fully resolved. The two complexes apparently stay associated with chromosomes after the sister chromatids separate from each other in anaphase. At least one of the subunits of condensin I is known to be a direct target of a cyclin-dependent kinase

Cyclin-dependent kinase

thumb|350px|Schematic of the cell cycle. outer ring: I=[[Interphase]], M=[[Mitosis]]; inner ring: M=Mitosis; G1=[[G1 phase|Gap phase 1]]; S=[[S phase|Synthesis]]; G2=[[G2 phase|Gap phase 2]]...

 (Cdk).

Biochemical activities

Purified condensin I introduces positive superhelical tension into DNA in an ATP-hydrolysis-dependent manner. It also displays a DNA-stimulated ATPase activity in vitro.

Relatives

Eukaryotic cells have two additional classes of SMC protein

SMC protein

SMC proteins represent a large family of ATPases that participate in many aspects of higher-order chromosome organization and dynamics. SMC stands for Structural Maintenance of Chromosomes.-Prokaryotic:...

complexes. Cohesin

Cohesin

Cohesin is a protein complex that regulates the separation of sister chromatids during cell division, either mitosis or meiosis.- Structure :...

contains SMC1 and SMC3 and is involved in sister chromatid cohesion. The SMC5/6 complex contains SMC5 and SMC6 and is implicated in recombinational repair.