Practice question

Histone code marks specific chromatin states. H3 lysine 9 di and trimethylation catalyzed by SUV39H1 and SUV39H2 methyltransferases creates high affinity binding site for heterochromatin protein 1 alpha via its chromodomain, inducing spreading, compaction and transcriptional repression. H3K9 trimethylation enriched at pericentric satellite repeats, subtelomeric repeats and retrotransposons characterizes constitutive heterochromatin, contrasting with H3K4 trimethylation at active promoters. HP1 oligomerization and interaction with DNMTs maintain domain stability. Disruption causes position effect variegation, ectopic transcription and chromosome missegregation defects compromising genome stability severely.