Chromosome biology lecture 13

Question 1

Chromatin structure

Answer 1

• Chromatin → nucleosome → fibre
• Nucleosome = H2A,B,H3,H4
• N terminal tails protrude out = target for PTM which Δ chromatin structure
• Acetylation = -vely charged PTM, relax DNA (also =ve)

Question 2

Phosphorylation of histone variant H2AX

Answer 2

• Variant of H2A that has 15aa CT extension inc SQE motif
• H2AX phosph in response to DSB by ATM, ATR or DNA-Pk
• Staining pattern in nuclei
• After repair, H2AX is dephosph by PP2A
• Fast vs slow kinetics

Question 3

ATM-dependent phosphorylation of KAP-1

Answer 3

• Heterochromatin → repressors bind + recruit co-repressors like KAP-1
• In turn recruits chromatin modifying E like methyl transferases
• Knockout KAP-1
• ATM inhibits KAP-1 by phosph, can facilitate repair by relieving heterochromatin formation