LIFESCI 3 Lecture Notes - Lecture 14: Heterochromatin, Chromodomain, Bromodomain
Document Summary
Experiment determines how dna is wrapped: mnase (micrococcal nuclease) degrades unprotected dna, experiment: random & limited digestion of dna -> nucleosomal repeat length in increments of 150 bp. If let it degrade every bit of unprotected dna -> single big band at 150 bp. Nucleosome: 1 nucleosome made of 8 histones (4 core histones * 2 sets, about 160 bp of dna wrapped around it twice, histones have globular structure & tails (stream of amino acid) sticking out (n or c terminus) Tails can be modified to increase/decrease their affinity to dna -> changes gene expression (change charge) Tails are sites of post-translational modification: histone tails are positively charged, interacts with dna. Lysine in tail (lysine is positively charged amino acid) (cid:862)hat(cid:863) (histone acetyl transcripase) enzyme does acetylation (adds acetyl group on lysine) -> neutral lysine. Hdac enzyme -> deacetylation -> restores positive charge. Methylating lysine recruits higher order chromatin remodeling; represses gene expression (does not change charge)
