lo 3 Evidence for the histone code in transcription control

Is H3K4me1 essential for life?

Yes, double catalytic mutant of MLL3/4 is early embryonic lethal

What does H3K4me1 correlate with?

Transcriptionally engaged enhancer elements

What does H3K27ac correlate with?

Transcriptionally engaged enhancer elements

What complex is responsible for H3K4 methylation?

COMPASS complex

What does MLL3 and MLL4 do?

They are histone H3K4 monomethyltransferases that facilitate enhancer activity

Does loss of H3K4me1 from enhancers cause major effects on transcription in static cell models?

No, it causes surprisingly minor effects on transcription

What happens when MLL3/4 proteins are lost?

Strong depletion of enhancer Pol II occupancy and eRNA synthesis, with downregulation of target genes

What is the role of H3K4me1 in cell fate transitions?

It is essential for transition from one cell fate to another, i.e., differentiation

What protein complex does DPF1-3 (reader of H3K4me1) help recruit?

The BAF (SWI/SNF) complex

What is the BAF complex critical for?

Gene/enhancer activation through remodelling nucleosomes

What is the effect of CBP/p300 activity on transcription?

They acetylate histones to promote chromatin accessibility and activate transcription

Is H3K27ac essential for RNA Polymerase machinery binding?

No, loss of H3K27ac is dispensable for binding of RNA Polymerase machinery (RPB1)

Does loss of H3K27ac affect transcriptional control of target genes?

No, it does not affect transcriptional control of target genes of affected enhancers

What is a limitation of studies using H3K27R mutants?

They don't take into account how this affects H3K27me3 (repressive modification) or the redundancy of histone acetylation modifications

What is the RNA Pol II CTD code?

Phosphorylation of the C-terminal domain at specific positions controls RNA Pol II activity

What is Ser5 phosphorylation of RNA Pol II CTD linked with?

Initiating and paused forms of RNA Pol II

What is Ser2 phosphorylation of RNA Pol II CTD linked with?

Elongating and terminating forms of RNA Pol II

Is H3K4me3 required for RNA Pol II elongation?

Yes, it is required for pause release

What happens in the absence of H3K4me3 regarding RNA Pol II?

Transition from RNA Pol II pausing to elongating forms is disrupted

What is H3K36me3 associated with?

Active gene bodies (not promoters)

What is a limitation of the study on H3K4me3 and RNA Pol II elongation?

The study uses total knockout, not catalytic mutants

What is the order of events in enhancer activation?

1

1) H3K4me1 deposited by MLL3/4,

What is the order of events in enhancer activation?

2)

P300/CBP deposit H3K27ac,

What is the order of events in enhancer activation?

3)

H3K4me1 recruits BAF complex,

What is the order of events in enhancer activation?

4)

Bromodomain proteins bind acetylation marks,

What is the order of events in enhancer activation?

5)

Mediator is recruited for looping,

What is the order of events in enhancer activation?

6)

General transcriptional machinery binds,

What is the order of events in enhancer activation?

7)

Tissue specific gene expression

What is eRNA?

Enhancer RNA produced from active enhancers

Can H3K4me1 alone instruct transcription?

depends on cellular context,

histone residue position,

presence of redundant histone modifications,