Nanowires of layered van der Waals (vdW) crystals are of interest due to structural characteristics and emerging properties that have no equivalent in conventional 3D crystalline nanostructures. Here, vapor−liquid−solid growth, optoelectronics, and photonics of GaS vdW nanowires are studied. Electron microscopy and diffraction demonstrate the formation of high-quality layered nanostructures with different vdW layer orientation. GaS nanowires with vdW stacking perpendicular to the wire axis have ribbon-like morphologies with lengths up to 100 μm and uniform width. Wires with axial layer stacking show tapered morphologies and a corrugated surface due to twinning between successive few-layer GaS sheets. Layered GaS nanowires are excellent wide-bandgap optoelectronic materials with E g = 2.65 eV determined by single-nanowire absorption measurements. Nanometer-scale spectroscopy on individual nanowires shows intense blue band-edge luminescence along with longer wavelength emissions due to transitions between gap states and photonic properties such as interference of confined waveguide modes propagating within the nanowires. The combined results show promise for applications in electronics, optoelectronics, and photonics, as well as photo-or electrocatalysis owing to a high density of reactive edge sites, and intercalation-type energy storage benefiting from facile access to the interlayer vdW gaps.
In situ liquid cell electron microscopy of the pH-driven assembly of single stranded DNA-functionalized Au nanoparticles in aqueous solution.
21Epigenetic variants of the archaeon Sulfolobus solfataricus called SARC have evolved heritable traits 22 including extreme acid resistance, enhanced genome integrity and a conserved "SARC" transcriptome 23 related to acid resistance. These traits appear to result from altered chromatin protein function related 24 to the heritable hypomethylation of chromatin proteins Cren7 and Sso7D. To clarify how this might 25 occur, ChIPseq and Affinity Purification Mass Spectrometry (AP-MS) were used to compare Cren7 and 26 Sso7D genome binding sites and protein networks between lineages (wild type and SARC) and culture 27 pH (pH 1 and 3). All SARC transcriptome loci were bound by these chromatin proteins but with invariant 28 patterns indicating binding alone was insufficient to mediate the SARC traits. In contrast, chromosome 29 association varied at other loci. Quantitative AP-MS was then used to identify protein interaction 30 networks and these included transcription and DNA repair proteins implicated in the evolved heritable 31 traits that varied in abundance between SARC and wild type strains. Protein networks included most of 32 the S-adenosylmethionine (SAM) synthesis pathway including serine hydroxymethyltransferase (SHMT), 33 whose abundance varied widely with culture pH. Because epigenetic marks are coupled to SAM pools 34 and oxidative stress in eukaryotes, occurrence of a similar process was investigated here. Archaeal SAM 35 pools were depleted by treatment with SAM pathway inhibitors, acid or oxidative stress and, like 36 eukaryotes, levels were raised by vitamin B12 and methionine supplementation. We propose that in 37 archaea, oxidation-induced SAM pool depletion acting through an SHMT sensor, drove chromatin 38 protein hypomethylation and thereby protein network changes that established the evolved SARC 39 epigenetic traits. 40 Significance Statement 41Archaea and eukaryotes share many molecular processes, including chromatin-mediated epigenetic 42 inheritance of traits. As with eukaryotes, archaeal protein complexes were formed between trait-related 43 proteins and chromatin proteins, subject to chromatin protein methylation state. Oxidation-induced 44 depletion of S-adenosylmethionine (SAM) pools likely resulted in chromatin protein hypomethylation. 45 Subsequent chromatin enrichment of serine hydroxymethyltransferase as a response to oxidative stress 46 could modulate methylation at specific genomic loci. The interplay between archaeal metabolism and 47 chromatin appear consistent with patterns observed in eukaryotes and indicate the existence of an 48 ancient oxidation signal transduction pathway controlling epigenetics. 49 50 Immunoprecipitation for ChIP-Seq. Triplicate crosslinked cell pellets were sonicated and subjected to 105 chromatin immunoprecipitation using polyclonal antibody serum for Cren7 or Sso7D as described 106 previously (30) with alterations described in and SI Appendix, Supplemental Methods. 107ChIP-Seq and data analysis. DNA samples were blunt ended, A-tailed, ligated to barcoded a...
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