The Establishment of Active Chromatin Domains

It has become obvious during the past several yearsthat the true template for transcription in eukaryotes ischromatin, not bare DNA, and that the processes thatmodify chromatin structure are integral parts of the transcription mechanism. Modification of histones by acetylation, or the ATP-dependent disruption of nucleosomesby a variety of protein complexes, can alter transcriptionrates at specific genes. Enzymes responsible for histoneacetylation or deacetylation can be part of a complexwhich also contains DNA sequence-specific transcriptionfactors, and activation or repression is coupled to bindingof the appropriate acetylase or deacetylase. The involvement of the transcription factor assures that the histonemodification is targeted to the proper gene and may alsomean that the effects of histone modification are confinedto a relatively small region in the neighborhood of thepromoter...