H1.X with different properties from other linker histones is required for mitotic progression

AbstractWe report here the characterization of H1.X, a human histone H1 subtype. We demonstrate that H1.X accumulates in the nucleolus during interphase and is distributed at the chromosome periphery during mitosis. In addition, the results of fluorescence recovery after photobleaching indicate that the exchange of H1.X on and off chromatin is faster than that of the other H1 subtypes. Furthermore, RNA interference experiments reveal that H1.X is required for chromosome alignment and segregation. Our results suggest that H1.X has important functions in mitotic progression, which are different from those of the other H1 subtypes

Nucleolin functions in nucleolus formation and chromosome congression

Ma N., Matsunaga S., Takata H., et al. Nucleolin functions in nucleolus formation and chromosome congression. Journal of Cell Science, 120, 12, 2091. https://doi.org/10.1242/jcs.008771

PHB2 Protects Sister-Chromatid Cohesion in Mitosis

SummaryCohesion between sister chromatids is essential for proper chromosome segregation in mitosis. In vertebrate mitotic cells, most cohesin is removed from the chromosome arms [1–4], but centromeric cohesin is protected by shugoshin until the onset of anaphase [5]. However, the mechanism of this protection of centromeric cohesion is not well understood. Here, we demonstrate that prohibitin 2 (PHB2) is involved in the regulation of sister-chromatid cohesion during mitosis in HeLa cells. PHB2 is an evolutionarily conserved protein in eukaryotes and has multiple functions, such as transcriptional regulation and cell viability and development [6–8]. However, its functions in mitosis have not yet been determined. We show that depletion of PHB2 by RNA interference (RNAi) causes premature sister-chromatid separation and defects in chromosome congression accompanied by mitotic arrest by spindle-checkpoint activation. In the absence of PHB2, cohesin is dissociated from centromeres during early mitosis, although the centromeric localization of shugoshin is preserved. Thus, our findings suggest that, in addition to the shugoshin, PHB2 is also required to protect the centromeric cohesion from phosphorylation by Plk1 during early mitosis and that its function is essential for proper mitotic progression

Mixed alkali-ion transport and storage in atomic-disordered honeycomb layered NaKNi2TeO6

Honeycomb layered oxides constitute an emerging class of materials that show interesting physicochemical and electrochemical properties. However, the development of these materials is still limited. Here, we report the combined use of alkali atoms (Na and K) to produce a mixed-alkali honeycomb layered oxide material, namely, NaKNi2TeO6. Via transmission electron microscopy measurements, we reveal the local atomic structural disorders characterised by aperiodic stacking and incoherency in the alternating arrangement of Na and K atoms. We also investigate the possibility of mixed electrochemical transport and storage of Na+ and K+ ions in NaKNi2TeO6. In particular, we report an average discharge cell voltage of about 4 V and a specific capacity of around 80 mAh g–1 at low specific currents (i.e., < 10 mA g–1) when a NaKNi2TeO6-based positive electrode is combined with a room-temperature NaK liquid alloy negative electrode using an ionic liquid-based electrolyte solution. These results represent a step towards the use of tailored cathode active materials for “dendrite-free” electrochemical energy storage systems exploiting room-temperature liquid alkali metal alloy materials

Physical and functional interaction between DDB and XPA in nucleotide excision repair

Damaged DNA-binding protein (DDB), consisting of DDB1 and DDB2 subunits recognizes a wide spectrum of DNA lesions. DDB is dispensable for in vitro nucleotide excision repair (NER) reaction, but stimulates this reaction especially for cyclobutane pyrimidine dimer (CPD). Here we show that DDB directly interacts with XPA, one of core NER factors, mainly through DDB2 subunit and the amino-acid residues between 185 and 226 in XPA are important for the interaction. Interestingly, the point mutation causing the substitution from Arg-207 to Gly, which was previously identified in a XP-A revertant cell-line XP129, diminished the interaction with DDB in vitro and in vivo. In a defined system containing R207G mutant XPA and other core NER factors, DDB failed to stimulate the excision of CPD, although the mutant XPA was competent for the basal NER reaction. Moreover, in vivo experiments revealed that the mutant XPA is recruited to damaged DNA sites with much less efficiency compared with wild-type XPA and fails to support the enhancement of CPD repair by ectopic expression of DDB2 in SV40-transformed human cells. These results suggest that the physical interaction between DDB and XPA plays an important role in the DDB-mediated NER reaction

Evolutionary aspects of a unique internal mitochondrial targeting signal in nuclear-migrated rps19 of sugar beet (Beta vulgaris L.)

The endosymbiotic theory postulates that many genes migrated from endosymbionts to the nuclear genomes of their hosts. Some migrated genes lack presequences directing proteins to mitochondria, and their mitochondrial targeting signals appear to be inscribed in the core coding regions as internal targeting signals (ITSs). ITSs may have evolved after sequence transfer to nuclei or ITSs may have pre-existed before sequence transfer. Here, we report the molecular cloning of a sugar beet gene for ribosomal protein S19 (Rps19; the first letter is capitalized when the gene is a nuclear gene). We show that sugar beet Rps19 (BvRps19) is an ITS-type gene. Based on amino-acid sequence comparison, dicotyledonous rps19s (the first letter is lower-cased when the gene is a mitochondrial gene), such as tobacco rps19 (Ntrps19), resemble an ancestral form of BvRps19. We investigated whether differences in amino-acid sequences between BvRps19 and Ntrps19 were involved in ITS evolution. Analyses of the intracellular localization of chimaeric GFP-fusion proteins that were transiently expressed in Welsh onion cells showed that Ntrps19-gfp was not localized in mitochondria. When several BvRps19-type amino acid substitutions, none of which was seen in any other angiosperm rps19, were introduced into Ntrps19-gfp, the modified Ntrps19-gfp became localized in mitochondria, supporting the notion that an ITS in BvRps19 evolved following sequence transfer to nuclei. Not all of these substitutions were seen in other ITS-type Rps19s, suggesting that the ITSs of Rps19 are diverse. (c) 2013 Elsevier B.V. All rights reserved

Post-translational mechanisms are associated with fertility restoration of cytoplasmic male sterility in sugar beet

Genetic conflict between cytoplasmically inherited elements and nuclear genes due to their different transmission patterns can be seen in cytoplasmic male sterility (CMS), the mitochondrion-encoded inability to shed functional pollen. CMS is associated with a mitochondrial ORF absent from non sterility-inducing mitochondria (S-orf). Nuclear genes that suppress CMS are called restorer-of-fertility (Rf) genes. Post-transcriptional and translational repression of S-orf mediates the molecular action of Rf that encodes a class of RNA-binding proteins having pentatricopeptide repeat (PPR) motifs. Besides the PPR-type of Rfs, there are also non-PPR Rfs, but the molecular interactions between non-PPR Rf and S-orf have not been described. In this study, we investigated the interaction of sugar beet bvORF20, a non-PPR Rf, with preSatp6, the sugar beet S-orf. Anthers expressing bvORF20 contained a protein that interacted with preSATP6 protein. Analysis of anthers and transgenic calli expressing a FLAG-tagged bvORF20 suggested binding of preSATP6 to bvORF20. To see the effect of bvORF20 on preSATP6, which exists as a 250-kDa protein-complex in CMS plants, signal bands of preSATP6 in bvORF20-expressing and non-expressing anthers were compared by immunoblotting combined with Blue Native polyacrylamide gel electrophoresis. The signal intensity of the 250-kDa band decreased significantly and 200- and 150-kDa bands appeared in bvORF20-expressing anthers. Transgenic callus expressing bvORF20 also generated the 200- and 150-kDa bands. The 200-kDa complex likely includes both preSATP6 and bvORF20. Post-translational interaction between preSATP6 and bvORF20 appears to alter the higher order structure of preSATP6 that may lead to fertility restoration in sugar beet