p300 forms a stable, template-committed complex with chromatin: role for the bromodomain.

Area of Science:

• Molecular Biology
• Epigenetics
• Gene Regulation

Background:

• Understanding how coactivator proteins interact with active promoters in chromatin is key to transcriptional regulation.
• The coactivator p300 plays a significant role in gene expression, but its precise interaction with chromatin is not fully understood.

Purpose of the Study:

• To investigate the functional association of the coactivator p300 with chromatin templates.
• To elucidate the role of the p300 bromodomain in chromatin binding and histone interactions.

Main Methods:

• Biochemical assays, including in vitro transcription template competition assays.
• Analysis of p300-chromatin complex formation and dependence on incubation time and activator proteins.
• Examination of the binding properties of the isolated p300 bromodomain to free and nucleosomal histones.

Main Results:

• p300 forms a stable, template-committed complex with chromatin during transcription, independent of activator proteins.
• p300 directly binds to chromatin, requiring its bromodomain for this interaction.
• The p300 bromodomain preferentially binds free histone H3 over nucleosomal histones.

Conclusions:

• The stable association of p300 with chromatin is mediated, in part, by its bromodomain binding to histones.
• This bromodomain-histone interaction is critical for p300 function in transcriptional regulation.
• A model is proposed where p300 exhibits both activator-dependent targeting and activator-independent chromatin binding.