Base-pair geometry and the complementarity between the bases cannot reach the extraordinarily high levels of accuracy

TLS Online TPP Program

#Id: 6870

#Unit 3. Fundamental Processes

Rap1 recruits Sir4 on acetylated histones, then recruits both its binding partner Sir3 and the HDAC Sir2. 

Sir3 and Sir4 then interact directly with histones H3 and H4. Once Sir3 and Sir4 have bound to histones H3 and H4, 

Sir2 deacetylates histones

Sir2-dependent deacetylation represses transcription.

TLS Online TPP Program

#Id: 6871

#Unit 3. Fundamental Processes

TLS Online TPP Program

#Id: 6872

#Unit 3. Fundamental Processes

RNA-induced silencing complex (RISC/RITS) remodeling complexes to chromatin to form heterochromatin in telomeres.

The siRNA complex promotes methylation of histone H3K9 by the Clr4 methyltransferase (also known as KMT1, a homolog of Drosophila Su[Var]3–9). H3K9 methylation recruits the S. pombe homolog of HP1, Swi6.

TLS Online TPP Program

#Id: 6873

#Unit 3. Fundamental Processes

In human cells, the centromere- specific protein CENP-B is required to initiate modifications of histone H3 (deacetylation of K9 and K14, followed by methylation of K9) that trigger an association with HP1 that leads to the formation of heterochromatin in the region.

TLS Online TPP Program

#Id: 6874

#Unit 3. Fundamental Processes

Heterochromatin and RNAi are required to establish the human CenH3 homolog, CENP-A, at centromeres.

TLS Online TPP Program

#Id: 6875

#Unit 3. Fundamental Processes

Polycomb or Pc-G proteins do not initiate repression, but they are responsible for maintaining it.