lecture 3 recap Flashcards
what are the 3 ways activators promote transcription
- promote binding of an additional activator.
- stimulate complex assembly (pol II to bind to TATA)
- release stalled RNA pol II
what small protein composes chromatin
histones
what are the 2 types of histones
core histones and linker histones
what are the 4 types of core histones
H2A, H2B, H3, H4
core histones have a globular domain made up of
alpha helices and loops
core histones also have an N terminal rich in
Lysine and arginine
what does the globular domain folds into
a histone fold
the histone folds from different core histones interacts to form what?
handshake interaction
what is an octamer
central H3-H4 tetramer and 2 flanking H2A-H2B dimers
the core histones form repeating units called
nucleosomes
what is a nucleosome
around 247bp of DNA wrapped twice around an octamer of histone proteins
DNA passes directly from one nucleosome to
the next nucleosome
what binds to the DNA between nucleosomes
linker histones such as histone H1
what are the 3 main mechanisms for modulating the structure if chromatin
histone variants
post-translational modification of histones
ATP dependent chromatin remodelling
histone variants are
alternative histones to the core histones
all histones have variants except
H4
histone variants change what
the structural and functional properties of the nucleosome
post translational modification of histones is
modification of the N terminal tails
what are examples of modification of the N terminal tails
acetylation
methylation
ubiquitination
phosphorylation
the modification state of the histone dictates the
transcriptional state of the DNA, referred to as the histone code
what is histone acetylation mediated by
HATs (histone acetyl transferases)
histone acetylation occurs on?
lysine residues in the N terminal tail
what is histone acetylation reversed by
HDACs (histone deacetylases) through hydrolysis
high levels of acetylation correlates with
high levels of transcription
what are the 2 major types of HATs
GNAT family and MYST family
how are HATs recruited to chromatin
HATs contain a specific subunit that interacts with activators therefore the activator brings the HATs to the promoters
acetylation causes what change to the lysine
the charge to be reduced
therefore the positively charge lysine can no longer interact with what?
negatively charged DNA making the chromatin less compact and easier for transcription to occur
acetylation of lysine also allows which proteins to recognise the DNA
proteins containing bromodomains
what do proteins containing bromodomains promote
transcription
bromodomain Bdf1 binds to what
acetylated H4
what does this recruit
TFIID
histone methylation can occur on
lysine and arginine residues
what proteins methylates lysine
histone lysine methyl transferases (HKMTs)
HKMTs add up to how many methyl groups
3
what reverses the methylation of lysine
lysine demethylases
does methylation affect the charge of the lysine
no, meaning it only has a small affect of chromatin structure
methylated lysines act as a binding site for binding modules e.g.
chromodomains
methylation on H3 Lys9 and H3 Lys27 causes
repression of transcription
