The key difference between cohesin and condensin is that cohesin is a tetrameric protein complex which holds sister chromatids tightly together while condensin is a pentameric protein complex required for chromosome condensation.
Cohesin and condensin are two multi-component proteins that are important in sister chromatid segregation in cell division. Cohesin is essential during the metaphase, while condensin is essential during the anaphase. When going from metaphase to anaphase, condensin replaces cohesin and allows sister chromatids to reach their respective poles. Structurally and functionally, these two proteins differ from each other.
CONTENTS
1. Overview and Key Difference
2. What is Cohesin
3. What is Condensin
4. Similarities Between Cohesin and Condensin
5. Side by Side Comparison – Cohesin vs Condensin in Tabular Form
6. Summary
What is Cohesin?
Cohesin is a protein that holds sister chromatids together after DNA replication until anaphase occurs, and it is the right time to separate sister chromatids from each other. Structurally, cohesin is a multi-subunit protein complex which actually has four core subunits. Out of the four subunits, two are SMC proteins (SMC1 (structural maintenance of chromosome protein 1) and SMC3 (structural maintenance of chromosome protein 3), which have two main structural domains as head and hinge domains. Other two subunits are two long coiled-coil molecules. Due to cohesin protein, sister chromatids segregate to two poles correctly. Otherwise, cells cannot control the segregation of sister chromatids into each pole during the anaphase.
Figure 01: Cohesin
Cohesin also facilitates the attachment of spindle fibres to chromosomes. In addition, cohesin mediates DNA repairing by recombination.
What is Condensin?
Condensin is a pentameric protein complex needed for chromosome condensation. It consists of five subunits, including two SMC proteins and three auxiliary subunits. SMC proteins in condensing are SMC2 and SMC4. Condensin fulfils several functions in genome regulation, including mitotic and meiotic division, DNA repair, transcriptional control, and chromosome condensation.
Figure 02: Condensins
There are two types of condensins as condensin I and condensin II. Condensin I regulates the timing of chromosome condensation while condensin II facilitates the compaction of the chromosome loops along the sister chromatid axes.
What are the Similarities Between Cohesin and Condensin?
- Cohesin and condensin are proteins that act as molecular cross-linkers.
- Both cohesion and condensin are useful in chromosome segregation.
- They are also essential for mitotic chromosome architecture, the regulation of sister chromatid pairing, DNA repair and replication, and the regulation of gene expression.
- They are close functional and structural relatives.
- Both are multi-component molecules.
- SMC proteins are components of both cohesion and condensin.
- They are ring-like molecules.
What is the Difference Between Cohesin and Condensin?
Cohesin holds replicated sister chromatids together until they separate at anaphase while condensin reorganizes chromosomes into their highly compact mitotic structure. So, this is the key difference between cohesin and condensin. Furthermore, cohesin is a tetramer composed of four subunits, while condensing is a pentameric protein composed of five subunits.
The below infographic summarizes the difference between cohesin and condensin.
Summary – Cohesin vs Condensin
Cohesin and condensin are structural and functional relatives, which are multi-component proteins. They are essential for separating identical copies of the genome into daughter cells during cell division. Both contain SMC proteins, and they are ring-like structures. However, cohesin is a tetrameric protein while condensin is a pentameric protein. Furthermore, cohesin contains SMC1 and SMC3 while condensin contains SMC2 and SMC4. Thus, this summarizes the difference between cohesin and condensin.
Reference:
1. Makrantoni, Vasso, and Adele L Marston. “Cohesin and Chromosome Segregation.” Current Biology: CB, Cell Press, 18 June 2018, Available here.
2. “Condensin.” Condensin – an Overview | ScienceDirect Topics, Available here.
Image Courtesy:
1. “Cohesin” By Blastwizard at English Wikipedia – Transferred from en.wikipedia to Commons by Vojtech.dostal., (CC BY-SA 3.0) via Commons Wikimedia
2. “3condensins2(en)” By Ascendinglotus2 – Own work (CC BY-SA 3.0) via Commons Wikimedia