Nuclear receptors are ligand inducible TFs. They recruit general TFs to PIC or bind coactivators. NR binding to coactivators is mediated through activation domains, AF-1 and AF-2.
In a binding model, activation domain rapidly binds coactivator via weak electrostatic interactions. Complex slowly converts yo more stable form. Activation domain folds into defined structure.
The metazoan mediator coactivator compelx as an integrative hub for transcriptioanl regulation
|Involvement of Mediator in multiple steps of transcription|
Groucho gene (gro) encodes a tnrascriptional corepressor with homologs with all metazoanz. Gro lacks a DNA-binding domain. It is recruited to DNA by spec proitein-protein interactions with DNA-bound repressors. Gro is essnetial in develpomental processes eg segmentation, dorsal/ventral and terminal pattern formtaion, neurogenesis, sex determination and patterning of compound eye.
Gro interacts preferentially with hypoacetylated histones. A western blot using Abs that recognise acetlated forms of histones H3 and H4 shows that no acetylated protein is detected antiacetylated H3 or H4.
N-terminal region of Gro excluding WD-repeat domain is required for efficient binding to core histones. Use GST pulldown assay.
Histone modifications: now summoning sumoylation
Sumoylation stimulates activity eg HSF1 and tumour suppressor p53/. It correlates with decreased transcription and repression of target genes.
H4 histone is sumoylated. Expression of reporter is decreased by targting EBC9 which conjugates sUMO to its substrate.
SUMO-H4 associates with chromatin.
Gene activation correlates with acetlation by HATs. Once gene is transcribed, its additivity must be attenuated and repressed. Signal for recruitment of sumoylating enzymes may be acetylation. H4 sumpoylation increases with increasing H4 acetylation. HDAC mediates removal of acetyl groups recruited by DNA bound repressors. Repression by histone methyltransferase methylation. Required for HP1 binding which enables chromatin condensation.