Combinatorial readout of histone H3 modifications specifies localization of ATRX to heterochromatin.

Accurate read-out of chromatin modifications is essential for eukaryotic life. Mutations in the gene encoding X-linked ATRX protein cause a mental-retardation syndrome, whereas wild-type ATRX protein targets pericentric and telomeric heterochromatin for deposition of the histone variant H3.3 by means of a largely unknown mechanism.

A method for genetically installing site-specific acetylation in recombinant histones defines the effects of H3 K56 acetylation.

Lysine acetylation of histones defines the epigenetic status of human embryonic stem cells and orchestrates DNA replication, chromosome condensation, transcription, telomeric silencing, and DNA repair. A detailed mechanistic explanation of these phenomena is impeded by the limited availability of homogeneously acetylated histones. We report a general method for the production of homogeneously and site-specifically acetylated recombinant histones by genetically encoding acetyl-lysine.

30 nm chromatin fibre decompaction requires both H4-K16 acetylation and linker histone eviction.

The mechanism by which chromatin is decondensed to permit access to DNA is largely unknown. Here, using a model nucleosome array reconstituted from recombinant histone octamers, we have defined the relative contribution of the individual histone octamer N-terminal tails as well as the effect of a targeted histone tail acetylation on the compaction state of the 30 nm chromatin fiber. This study goes beyond previous studies as it is based on a nucleosome array that is very long (61 nucleosomes) and contains a stoichiometric concentration of bound linker histone, which is essential for the formation of the 30 nm chromatin fiber.

Structural consequences of disease-causing mutations in the ATRX-DNMT3-DNMT3L (ADD) domain of the chromatin-associated protein ATRX.

The chromatin-associated protein ATRX was originally identified because mutations in the ATRX gene cause a severe form of syndromal X-linked mental retardation associated with alpha-thalassemia. Half of all of the disease-associated missense mutations cluster in a cysteine-rich region in the N terminus of ATRX. This region was named the ATRX-DNMT3-DNMT3L (ADD) domain, based on sequence homology with a family of DNA methyltransferases.

The human telomeric protein TRF1 specifically recognizes nucleosomal binding sites and alters nucleosome structure.

Telomeres are dynamic nucleoprotein structures that cap the ends of eukaryotic chromosomes. In humans, the long (TTAGGG)(n) double-stranded telomeric DNA repeats are bound specifically by the two related proteins TRF1 and TRF2, and are organized in nucleosomes. Whereas the role of TRF1 and TRF2 in telomeric function has been studied extensively, little is known about the involvement of telomeric nucleosomes in telomere structures or how chromatin formation may affect binding of the TRFs.

How the human telomeric proteins TRF1 and TRF2 recognize telomeric DNA: a view from high-resolution crystal structures.

Human telomeres consist of tandem arrays of TTAGGG sequence repeats that are specifically bound by two proteins, TRF1 and TRF2. They bind to DNA as preformed homodimers and have the same architecture in which the DNA-binding domains (Dbds) form independent structural units. Despite these similarities, TRF1 and TRF2 have different functions at telomeres.

Telomere architecture.

Telomeres are protein-DNA complexes that cap chromosome ends and protect them from being recognized and processed as DNA breaks. Loss of capping function results in genetic instability and loss of cellular viability. The emerging view is that maintenance of an appropriate telomere structure is essential for function.