Practice question
Question
Which histone mark is linked with heterochromatin?
Explanation
Constitutive heterochromatin at centromeres, telomeres and repetitive elements is demarcated by trimethylation of H3K9 catalyzed by Suv39h1, Suv39h2 and SetDB1 enzymes. H3K9me3 is recognized by chromodomain of HP1α, β and γ, which oligomerize through chromo-shadow domain, bridging nucleosomes and compacting arrays into transcriptionally inert domains. HP1 also recruits Suv39h1 to propagate mark and DNMT3B for DNA methylation, reinforcing silencing loop. Loss of H3K9me3 leads to repeat derepression, genome instability and developmental defects, underscoring central role in lineage commitment and transposon suppression.
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