LIFE SCIENCE

Detailed explanation-1: -Heterochromatin Protein 1 (HP1) is a transcriptional repressor that directly binds to the methylated lysine 9 residue of histone H3 (H3K9me), which is a hallmark histone modification for transcriptionally silenced heterochromatin.

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.