An acetylated form of histone H2A.Z regulates chromosome architecture in Schizosaccharomyces pombe.

Histone variant H2A.Z has a conserved role in genome stability, although it remains unclear how this is mediated. Here we demonstrate that the fission yeast Swr1 ATPase inserts H2A.Z (Pht1) into chromatin and Kat5 acetyltransferase (Mst1) acetylates it. Deletion or an unacetylatable mutation of Pht1 leads to genome instability, primarily caused by chromosome entanglement and breakage at anaphase. This leads to the loss of telomere-proximal markers, though telomere protection and repeat length are unaffected by the absence of Pht1. Strikingly, the chromosome entanglement in pht1Delta anaphase cells can be rescued by forcing chromosome condensation before anaphase onset. We show that the condensin complex, required for the maintenance of anaphase chromosome condensation, prematurely dissociates from chromatin in the absence of Pht1. This and other findings suggest an important role for H2A.Z in the architecture of anaphase chromosomes.

The Saccharomyces cerevisiae histone H2A variant Htz1 is acetylated by NuA4.

The histone H2A variant H2A.Z (Saccharomyces cerevisiae Htz1) plays roles in transcription, DNA repair, chromosome stability, and limiting telomeric silencing. The Swr1-Complex (SWR-C) inserts Htz1 into chromatin and shares several subunits with the NuA4 histone acetyltransferase. Furthermore, mutants of these two complexes share several phenotypes, suggesting they may work together. Here we show that NuA4 acetylates Htz1 Lys 14 (K14) after the histone is assembled into chromatin by the SWR-C. K14 mutants exhibit specific defects in chromosome transmission without affecting transcription, telomeric silencing, or DNA repair. Function-specific modifications may help explain how the same component of chromatin can function in diverse pathways.

Histone H4 lysine 91 acetylation a core domain modification associated with chromatin assembly.

The acetylation of the NH2-terminal tail of histone H4 by type B histone acetyltransferases (HATs) is involved in the process of chromatin assembly. Histone H4 associated with a nuclear type B HAT complex contains modifications in its globular core domain as well. In particular, acetylation was found at lysine 91. A mutation that alters this residue, which lies in the interface between histone H3/H4 tetramers and H2A/H2B dimers, confers phenotypes consistent with defects in chromatin assembly such as sensitivity to DNA damaging agents and derepression and alteration of silent chromatin structure. In addition, this mutation destabilizes the histone octamer, leading to defects in chromatin structure. These results indicate an important role for histone modifications outside the NH2-tail domains in the processes of chromatin assembly, DNA repair, and transcriptional silencing.

Cytokine traps: multi-component, high-affinity blockers of cytokine action.

Cytokines can initiate and perpetuate human diseases, and are among the best-validated of therapeutic targets. Cytokines can be blocked by the use of soluble receptors; however, the use of this approach for cytokines such as interleukin (IL)-1, IL-4, IL-6 and IL-13 that use multi-component receptor systems is limited because monomeric soluble receptors generally exhibit low affinity or function as agonists. We describe here a generally applicable method to create very high-affinity blockers called 'cytokine traps' consisting of fusions between the constant region of IgG and the extracellular domains of two distinct cytokine receptor components involved in binding the cytokine. Traps potently block cytokines in vitro and in vivo and represent a substantial advance in creating novel therapeutic candidates for cytokine-driven diseases.