Cell Biology

                               HAT Coactivator

A coactivator is a protein that increases gene expression by binding to an activator or transcription factor which contains a DNA binding domain. The coactivator is unable to bind DNA by itself.

The coactivator can enhance transcription initiation by stabilizing the formation of the RNA polymerase holoenzyme enabling faster clearance of the promoter. Coactivators also control elongation, RNA splicing, and termination and degradation of the coactivator-activator complex.

Some coactivators possess intrinsic histone acetyltransferase (HAT) activity, which acetylates histones and causes chromatin to relax in a limited region allowing increased access to the DNA. CBP and p300 are examples of coactivators with HAT activity. Coactivators work in high molecular weight complexes of 6-10 coactivator and coactivator-associated proteins.

Histone deacetylase 2 

Histone deacetylase 2 is an enzyme that in humans is encoded by the HDAC2 gene. This gene product belongs to the Histone deacetylase family. Histone deacetylases act via the formation of large multiprotein complexes and are responsible for the deacetylation of lysine residues on the N-terminal region of the core histones (H2A, H2B, H3 and H4). This protein also forms transcriptional repressor complexes by associating with many different proteins, including YY1, a mammalian zinc-finger transcription factor. Thus it plays an important role in transcriptional regulation, cell cycle progression and developmental events.

RNA-induced transcriptional silencing (RITS)

RNA-induced transcriptional silencing (RITS) is a form of RNA interference by which short RNA molecule such as a small interfering RNA (siRNA) trigger the downregulation of transcription of a particular gene or genomic region. This is usually accomplished by posttranslational modification of histon tails (methylation of lysine 9 of histone H3) which target the genomic region for heterochromatin formation. The protein complex that binds to siRNAs and interacts with the methylated lysine 9 residue of histones H3 is the RITS complex.

http://en.wikipedia.org/wiki/Histone_acetylation_and_deacetylation

http://archives.focus.hms.harvard.edu/2004/Feb20_2004/cell_biology.html