Trithorax-group proteins are chromatin regulatory proteins which generally act to maintain gene expression. This group of proteins is rather heterogeneous and contains members that form several multiprotein chromatin complexes. One main activity of the Trithorax complex is to activate transcription by inducing trimethylation of lysine 4 of histone H3 (H3K4me3) at specific regulatory site

Regulatory site

A regulatory site is a site on an allosteric protein to which a modulator molecule binds. A ligand-binding site on a receptor or enzyme distinct from the active site. Allosteric modulators alter enzyme activity by binding to the regulatory site. Also known as an "allosteric site"....

s in their target chromatin. This active state is reinforced by acetylation of histone H4. In addition, some Trithorax-group proteins have chromatin remodeling activity, using the energy of ATP to mobilize nucleosomes.

Polycomb-group proteins

Polycomb-group proteins

Polycomb-group proteins are a family of proteins first discovered in fruit flies that can remodel chromatin such that epigenetic silencing of genes takes place...

 are the repressive couterpart to the Trithorax group proteins in that they also bind to the chromatin at the Hox genes and act to induce trimethylation of lysine 27 of histone H3 (H3K27me3), to prevent acetylation at histone H4, and to counteract nuclesome remodeling, thus maintaining silent states of gene expression.

External links

• The Polycomb and Trithorax page of the Cavalli lab This page contains useful information on Polycomb and trithorax proteins, in the form of an introduction, links to published reviews, list of Polycomb and trithorax proteins, illustrative power point slides and a link to a genome browser showing the genome-wide distribution of these proteins in Drosophila melanogaster.