NUCLEAR MATRIX, DYNAMIC HISTONE ACETYLATION AND TRANSCRIPTIONALLY ACTIVE CHROMATIN

The nuclear matrix, the RNA-protein skeleton of the nucleus, has a rol e in the organization and function of nuclear DNA. Nuclear processes a ssociated with the nuclear matrix include transcription, replication a nd dynamic histone acetylation. Nuclear matrix proteins, which are tis sue and cell type specific, are altered with transformation and state of differentiation. Transcription factors are associated with the nucl ear matrix, with the spectra of nuclear matrix bound factors being cel l type specific. There is compelling evidence that the transcription m achinery is anchored to the nuclear matrix, and the chromatin fiber is spooled through this complex. Transcriptionally active chromatin doma ins are associated with dynamically acetylated histones. The energy ex haustive process of dynamic histone acetylation has several functions. Acetylation of the N-terminal tails of the core histones alters nucle osome and higher order chromatin structure. aiding transcriptional elo ngation and facilitating the binding of transcription factors to nucle osomes associated with regulatory DNA sequences. Histone acetylation c an manipulate the interactions of regulatory proteins that bind to the N-terminal tails of the core histones. Lastly, dynamic acetylation ma y contribute to the transient attachment of transcriptionally active c hromatin to the nuclear matrix. Reversible histone acetylation is cata lyzed by histone acetyltransferase and deacetylase, enzymes associated with the nuclear matrix. The recent isolation and characterization of histone acetyltransferase and deacetylase reveals that these enzymes are related to transcriptional regulators, providing us with new insig hts about how these enzymes are targeted to nuclear matrix sites engag ed in transcription.