Alterazione della cromatinaAlterazione della cromatina

Modificazione degli istoni

Rimodellamento della cromatina

Watson et al., BIOLOGIA MOLECOLARE DEL GENE, Zanichelli editore S.p.A. Copyright © 2005

Watson et al., BIOLOGIA MOLECOLARE DEL GENE, Zanichelli editore S.p.A. Copyright © 2005

Watson et al., BIOLOGIA MOLECOLARE DEL GENE, Zanichelli editore S.p.A. Copyright © 2005

Watson et al., BIOLOGIA MOLECOLARE DEL GENE, Zanichelli editore S.p.A. Copyright © 2005

Watson et al., BIOLOGIA MOLECOLARE DEL GENE, Zanichelli editore S.p.A. Copyright © 2005

Watson et al., BIOLOGIA MOLECOLARE DEL GENE, Zanichelli editore S.p.A. Copyright © 2005

Watson et al., BIOLOGIA MOLECOLARE DEL GENE, Zanichelli editore S.p.A. Copyright © 2005

Biologia molecolare - Robert F. Weaver Copyright © 2005 – The McGraw-Hill Companies srl

Chromatin modificationChromatin 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.

Watson et al., BIOLOGIA MOLECOLARE DEL GENE, Zanichelli editore S.p.A. Copyright © 2005

Attività di rimodellamento della cromatinaAttività di rimodellamento della cromatina(in vitro)(in vitro)

“Scivolamento” dei nucleosomi

Trasferimento dell’ottamero istonico ad un’altra molecola di DNA

Formazione di dinucleosomi

Alterazione della struttura nucleosomale

Watson et al., BIOLOGIA MOLECOLARE DEL GENE, Zanichelli editore S.p.A. Copyright © 2005

Watson et al., BIOLOGIA MOLECOLARE DEL GENE, Zanichelli editore S.p.A. Copyright © 2005

Tipi di complessi di rimodellamento della cromatinaTipi di complessi di rimodellamento della cromatina

SWI/SNF: Swi/Snf di lievitoRSC di lievito

ISWI: NURF di Drosofila

CHRAC di Drosofila ACF di Drosofila

CHD (Mi-2/NuRD)

INO80

Watson et al., BIOLOGIA MOLECOLARE DEL GENE, Zanichelli editore S.p.A. Copyright © 2005

Watson et al., BIOLOGIA MOLECOLARE DEL GENE, Zanichelli editore S.p.A. Copyright © 2005

Chromatin remodelingChromatin 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 TrithoraxPolycomb 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.