BIOL 202 Lecture Notes - Lecture 23: Lysine, Histone Code, Dna Replication
Document Summary
Post-translational (covalent modification) of histone tails i. e. acetylation and methylation. Amino-terminal ends of core histones protrude from the nucleosome covalent modifications of these tails can have profound effects on gene regulation: anetylation, methylation, phosphorylation, ubiquitination these mod. Affect: affinity for dna, binding of other regulatory proteins (histone code) 44 histone tail lysine residues per nucleosome available for modification by acetylation. Acetylation neutralizes positive charge in histone tails and weakens assoc. with dna (neg. charged: nh3. + turns into nh-co-ch3 during acetylation via hats (histone acetyl transferases. Reverse reaction catalyzed by hdacs (histone deacetylases) Hats activate transcription: hyperacetylation of lysines leads to looser histone-dna interaction, easing access by tfs, spec. transcriptional coactivators have the hat activity i. e. gcn5. Hdacs repress transcription: hypoacetylation of histones has the opposite effect. Tighter histone-dna interaction (inhibits transcription: specific transcriptional corepressors can have this activity (e. g. yeast. Rpd3) beta-interferon enhanceosome the beta-interferon enhancer is located between 2 nucleosomes. Enhanceosome assembles in response to viral infection.
