Epigenetics, or heritable changes not encoded in the DNA sequence, is a phenomenon important for an overall increase in the complexity of the genome without changes in gene sequence. Our complete genome is contained in each of our cells. Corneal cells are different than nerve cells due to a usage pattern of the genome that is maintained in a cellular memory of active or repressed genes. These “...

Histone acetyltransferase and histone deacetylase are enzymes responsible for histone acetylation and deacetylation, respectively, in which the histones are acetylated and deacetylated on lysine residues in the N-terminal tail and on the surface of the nucleosome core. These processes are considered the most important epigenetic mechanisms for remodeling the chromatin structure and controlling ...

The conserved histone variant H2AZ has an important role in the regulation of gene expression and the establishment of a buffer to the spread of silent heterochromatin. How histone variants such as H2AZ are incorporated into nucleosomes has been obscure. We have found that Swr1, a Swi2/Snf2-related adenosine triphosphatase, is the catalytic core of a multisubunit, histone-variant exchanger that...

In recent years, the chromatin field has witnessed a renewed interest in histone variants as pertaining to their structural role, but mainly because of the functional specificity they impart to chromatin. In this review, I am going to discuss several of the most recent structural studies on core histone (H2A.Bbd, H2A.Z, H2A.X, macroH2A, H3.3, CENP-A) and linker histone variants (histone H1 micr...

Ubiquitination & Sumoylation C e l l C y c l e & D N A T r a n s a c t i o n s In eukaryotes, the several meters long genomic DNA needs to be packed into chromosomes with a diameter of only several hundred micrometers. This is achieved through an elaborated scheme of packaging that starts with the formation of nucleosomes from DNA winding around an octamer core of histones H2A/H2B/H3/H4, foll...

The large genomes of higher eukaryotes suggest a need for stable packaging, particularly as most of the DNA does not code for proteins, and much consists of repetitious sequences, including remnants of invading retrotransposons, transposable elements and the like. Cytological studies first demonstrated that much of the repetitous DNA is packaged in a condensed form referred to as heterochromati...

Distinct histone lysine methylation marks are involved in transcriptional repression linked to the formation and maintenance of facultative heterochromatin, although the underlying mechanisms remain unclear. We demonstrate that the malignant-brain-tumor (MBT) protein L3MBTL1 is in a complex with core histones, histone H1b, HP1gamma, and Rb. The MBT domain is structurally related to protein doma...

In vitro analysis of DNA in chromatin is often important for understanding mechanisms of regulation of transcription and other processes that occur on DNA. The basic unit of chromatin is the nucleosome core, containing two copies each of the core histones H2A, H2B, H3, and H4 to form a histone octamer that wraps 145 base pairs of DNA in a left-handed superhelix. In vivo, chromatin is associated...

Chromatin on the inactive X chromosome (Xi) of female mammals is enriched for the histone variant macroH2A that can be detected at interphase as a distinct nuclear structure referred to as a macro chromatin body (MCB). Green fluorescent protein-tagged and Myc epitope-tagged macroH2A readily form an MCB in the nuclei of transfected female, but not male, cells. Using targeted disruptions, we have...