Chromatin modification Histone acetylation is associated with activation of gene expression. Deacetylated chromatin may have a more condensed structure. Transcription activators are associated with histone acetylase activities in large complexes. Transcription repressors are associated with histone deacetylase activities. Histone acetylases vary in their target specificity and we do not yet know whether acetylation affects transcription in a quantitative or qualitative way.
Attività di rimodellamento della cromatina (in vitro) “Scivolamento” dei nucleosomi Trasferimento dell’ottamero istonico ad un’altra molecola di DNA Formazione di dinucleosomi Alterazione della struttura nucleosomale
Chromatin remodeling Chromatin structure is stable and cannot be changed by altering the equilibrium of transcription factors and histones. There are several chromatin remodeling complexes that use energy provided by hydrolysis of ATP. The SWI/SNF, RSC, and NURF complexes all are very large; there are some common subunits. A remodeling complex does not itself have specificity for any particular target site, but must be recruited by a component of the transcription apparatus.
Polycomb and Trithorax Polycomb group proteins (Pc-G) perpetuate a state of repression through cell divisions. The PRE is a DNA sequence that is required for the action of Pc-G. The PRE provides a nucleation center from which Pc-G proteins propagate to maintain an inactive structure. No individual Pc-G protein has yet been found that can bind the PRE. Trithorax group proteins antagonize the actions of the Pc-G.