4 Chromatin remodelling and Transcriptional Repressiob

what is the catalytic subunit of SWI/SNF called?

Snf2

how does SWI/SNF remodel chromatin?

hydrolyses 1000 ATP molecules per minute in presence of DNA. Molecular motor uses energy from ATP hydrolysis to track along DNA and induce torsion. Results in disruption of histone-DNA interactions and movement of nucleosome.

How do ATP-dependent and HAT complexes co-operate?

HATs and ATP-dependent remodellers commenly recruited to same promoters. Bromodomains in Snf2 help tether it to acetylated nucleosomes

what kind of transcription factors are GTFs needed for?

Glucocorticoid and retinoid receptors, heat shock factor, MyoD etc

what roles fo SWI/SNF complexes have in humans

Cell cycle control via interaction with Rb and cyclin E. Develoment, deletion results in embrytonic lethality. Tumour supressor pathways, mutations are associated with a variety of tumour types.

How is SWI/SNF related to cancer?

implicated as a potent tumour supressors. One or more subunits mutated in 20% of all cancers. Mutations in multiple subunits prevalent sometimes

How do cells repress transcription?

exploit chromatin structure to bring about transcriptional repression mediated by recruitment of chromatin modifying factors.

what are some examples of chromatin remodelling factors?

HDACs, ATP-dependent remodellers, histone methylases (heterochromatin)

what is the difference between hyperacetylated and hypoacetylated?

Active regions of genome are hyperacetylated, repressed regions are hypoacetylated.

what do HDAC co-repressor complexes do?

recruited to promters by interaction with stie specific DNA binding proteins

What roles do ATP dependent remodelling complexes play?

Mediate transcriptional repression. Normal differentiation and tumourogenesis.

How do open and closed chromatin complexes relate to transcription?

Closed chromatin \= transcription off. Open chromatin \= transcription on

what are the biochemical features of heterochromatin?

hypoacetylation. specific histone H3 methylation. association of specific silencing factors

What do chromodomains recognise?

recognise and bind to methylated lysine residues

What is the role of HP1 in heterochromatin?

acts as platform the recruitment of further activities that prevent recruitment/activity of RNA pol II