Correlation between transition temperature, in-plane copper-oxygen bond length, and tilt/buckling of the CuO2 plane in cuprate superconductors

Correlation among transition temperature, in-plane Cu-O bond length, and tilt/buckling in cuprate superconductors were examined in detail. As for cuprates with a single CuO_2 layer, tilt structure was observed in the region, whose in-plane Cu-O length was 1.906-1.926 Å, and that the tilt structure drastically suppressed superconductivity. As for cuprates with double CuO_2 layers, all the compounds had buckling distortion in a CuO_5 pyramid. The degree of distortion was determined only by a kind of cation between the two facing CuO_5 pyramids, that is, calcium or yttrium. A higher transition temperature was obtained for a copper oxide with having larger Cu-O length and smaller buckling degree. A common feature of layered cuprates was the existence of three major classes distinguished by the cations Ba^, Sr^, and Ln^ occupying the 9-coordination sites

Histone H4 lysine 20 acetylation is associated with gene repression in human cells

Histone acetylation is generally associated with gene activation and chromatin decondensation. Recent mass spectrometry analysis has revealed that histone H4 lysine 20, a major methylation site, can also be acetylated. To understand the function of H4 lysine 20 acetylation (H4K20ac), we have developed a specific monoclonal antibody and performed ChIP-seq analysis using HeLa-S3 cells. H4K20ac was enriched around the transcription start sites (TSSs) of minimally expressed genes and in the gene body of expressed genes, in contrast to most histone acetylation being enriched around the TSSs of expressed genes. The distribution of H4K20ac showed little correlation with known histone modifications, including histone H3 methylations. A motif search in H4K20ac-enriched sequences, together with transcription factor binding profiles based on ENCODE ChIP-seq data, revealed that most transcription activators are excluded from H4K20ac-enriched genes and a transcription repressor NRSF/REST co-localized with H4K20ac. These results suggest that H4K20ac is a unique acetylation mark associated with gene repression