TLS Online TPP Program

#Id: 8855

#Unit 2. Cellular Organization

Cohesins are composed of four subunits: 

Smc1, Smc3, Scc1, and Scc3

TLS Online TPP Program

#Id: 8856

#Unit 2. Cellular Organization

Smc1 and Smc3 are members of the structural

maintenance of chromosomes (SMC) protein family, characterized by globular domains at the N- & C-termini connected by a long α helix, bind and hydrolyze ATP.

TLS Online TPP Program

#Id: 8857

#Unit 2. Cellular Organization

The ATPase domains interact with the proteins

Scc1 and Scc3, which together form a cohesin ring structure which embrace one or both copies of the replicated DNA.

TLS Online TPP Program

#Id: 8858

#Unit 2. Cellular Organization

Cohesin-mediated cohesion between sister chromatids is established by a two-step process:

1.Loading and unloading of cohesins

2. Stabilization of cohesins

TLS Online TPP Program

#Id: 8859

#Unit 2. Cellular Organization

During G1, 

cohesins associate with chromosomes by cohesin loading factors Scc2 and Scc4 and unloaded continuously by a cohesin associated complex Pds5 and Wap1 proteins. 

TLS Online TPP Program

#Id: 8860

#Unit 2. Cellular Organization

During S phase

DNA-bound G1 cohesins Convert into cohesive complexes by cohesin acetyl transferases (CoATs)

which acetylate Smc3 subunit & prevents unloading of cohesins by Pds5-Wapl, thereby stabilizing the cohesins on chromosomes.