EVERYDAY SCIENCE

Detailed explanation-1: -The proteins that link HP1 and replication include chromatin assembly factor (CAF1), a three subunit complex (p150, p60, and p48) that mediates histone H3 and H4 deposition onto newly replicated DNA in both euchromatic and heterochromatic regions during replication or DNA repair 62, 63.

Detailed explanation-2: -Heterochromatin Protein 1 (HP1) is a highly conserved protein that has been used as a classic marker for heterochromatin. HP1 binds to di-and tri-methylated histone H3K9 and regulates heterochromatin formation, functions and structure.

Detailed explanation-3: -The classical mechanism of HP1 mediated heterochromatin formation is as follows: H3K9me2/3 recruits HP1/ which then recruits the H3K9 methyltransferase SUV39H1. SUV39H1 then methylates more H3K9me2/3, creating a positive feedback loop spreading down the chromosome (Lachner et al., 2001).

Detailed explanation-4: -Recent studies show that HP1 proteins play an important role in heterochromatin by interacting with histones H3 and H4 and methyltransferase enzymes. The binding of the HP1 CD to poly-methylated H3 lysine 9 (H3K9me2/3) and H1. 4K26me85 triggers a silencing mechanism, resulting in the formation of heterochromatin.

Detailed explanation-5: -HP1 proteins are fundamental units of heterochromatin packaging that are enriched at the centromeres and telomeres of nearly all eukaryotic chromosomes with the notable exception of budding yeast, in which a yeast-specific silencing complex of SIR (silent information regulatory) proteins serve a similar function.