page_title: SMC3
section_title: Structure and interactions
hierarchical_section_title: SMC3 / Structure and interactions
caption_attribution_description: English: Structure of the SMC3-RAD21 interface (PDB 4UX3) from budding yeast (Gligoris et al. 2014)
context_page_description: Structural maintenance of chromosomes protein 3 is a protein that in humans is encoded by the SMC3 gene. SMC3 is a subunit of the Cohesin complex which mediates sister chromatid cohesion, homologous recombination and DNA looping. Cohesin is formed of SMC3, SMC1, RAD21 and either SA1 or SA2. In humans, SMC3 is present in all cohesin complexes whereas there are multiple paralogs for the other subunits.
  SMC3 is a member of the SMC protein family. Members of this family are key regulators of DNA repair, chromosome condensation and chromosome segregation.
context_section_description: The domain organisation of SMC proteins is evolutionarily conserved and is composed of an N-terminal Walker A motif, coiled-coil, "hinge", coiled-coil and a C-terminal Walker B motif. The protein folds back on itself to form a rod-shaped molecule with a heterodimerisation "hinge" domain at one end  and an ABC-type ATPase "head" at the other. These globular domains are separated by a ~50 nm anti-parallel coiled-coil. SMC3 and SMC1 bind via their hinge domains creating V-shaped heterodimers. The N-terminal domain of RAD21 binds to the coiled coil of SMC3 just above the head domain while the C-terminal domain of RAD21 binds the head domain of SMC1. This end to end binding of the SMC3-SMC1-RAD21 trimer creates a closed ring within which DNA can be entrapped. SA1 or 
  When DNA is replicated and sister chromatid cohesion is established SMC3 is acetylated on a pair of highly conserved lysines by ESCO1 and ESCO2. In budding yeast this modification is sufficient to stabilise cohesin on the DNA until mitosis but in animals, binding of sororin is also required.
  During meiosis, SMC3 forms cohesin complexes with SMC1ß, STAG3 and REC8 which generate cohesion between homologous chromosomes and sister chromatids.
caption: Structure of the interface between SMC3 (blue) and RAD21 (green) (PDB 4UX3) from budding yeast (Gligoris et al., 2014)
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