Lecture 7: Histone Tail Modification Learning Objectives

Explain the significance of the histone tails – where they lie on the nucleosome, what fraction of its mass they account for, and why they carry most of the modifications

Name the writers, erasers and readers of histone modifications and give two examples of each

Explain how acetylation of lysine affects chromatin, and name the reader domain that binds acetylated lysine

Say how many methyl groups a lysine can carry, name each state, and say what happens to the charge of the residue

Give one active and one repressive lysine methylation mark, and explain why the same chemical mark can mean opposite things

Explain how H3K9me3 recruits HP1 to silence a locus, and why other chromodomain proteins reading methylated lysine can instead activate transcription

Name the histone modifications covered here other than acetylation and methylation, and give the main effect of each

Define a bivalent domain, name the two marks that form it, and explain what it does for a pluripotent cell

Explain why marks do not act independently – the level of any mark is a steady state set by opposing writer and eraser activity, and one mark can license another, as H2BK120 ubiquitination licenses H3K4 and H3K79 methylation

Define the histone code hypothesis and give two reasons it remains a hypothesis rather than a principle, including the difficulty of separating cause from correlation