Single-molecule fluorescence imaging techniques reveal molecular mechanisms underlying deoxyribonucleic acid damage repair

Advances in single-molecule techniques have uncovered numerous biological secrets that cannot be disclosed by traditional methods. Among a variety of single-molecule methods, single-molecule fluorescence imaging techniques enable real-time visualization of biomolecular interactions and have allowed the accumulation of convincing evidence. These techniques have been broadly utilized for studying DNA metabolic events such as replication, transcription, and DNA repair, which are fundamental biological reactions. In particular, DNA repair has received much attention because it maintains genomic integrity and is associated with diverse human diseases. In this review, we introduce representative single-molecule fluorescence imaging techniques and survey how each technique has been employed for investigating the detailed mechanisms underlying DNA repair pathways. In addition, we briefly show how live-cell imaging at the single-molecule level contributes to understanding DNA repair processes inside cells

Experimental and computational investigations of the abnormal slow dissociation behavior of CH4 hydrate in the presence of Poly (N-vinylcaprolactam)

In this study, the dissociation behavior of CH4 hydrate in the absence and presence of poly(N-vinylcaprolactam) (PVCap) was closely investigated using a combination of experimental techniques, including in-situ Raman spectroscopy and high-pressure micro-differential scanning calorimetry (HP & mu;-DSC), and molecular dynamics (MD) simulations. The experimental results clearly demonstrated that CH4 hydrate dissociated more slowly and in two steps in the presence of PVCap. The MD simulations revealed that this slow and two-step dissociation was mainly due to the adsorption of PVCap onto the hydrate surface, which hindered the mass transfer of CH4 from the hydrate into the solution. The high viscosity and steric hindrance of PVCap also impeded the formation and growth of CH4 bubbles during the hydrate dissociation, contributing to the slower dissociation of CH4 hydrate in the PVCap solution. The broad and asymmetric shape of the last endothermic peak observed via HP & mu;-DSC was caused by the adsorption of PVCap during CH4 hydrate dissociation. The findings of this study provide valuable insights into the precise mechanism of hydrate dissociation in the presence of kinetic hydrate inhibitors

Deciphering Molecular Mechanism of Histone Assembly by DNA Curtain Technique

Chromatin is a higher-order structure that packages eukaryotic DNA. Chromatin undergoes dynamic alterations according to the cell cycle phase and in response to environmental stimuli. These changes are essential for genomic integrity, epigenetic regulation, and DNA metabolic reactions such as replication, transcription, and repair. Chromatin assembly is crucial for chromatin dynamics and is catalyzed by histone chaperones. Despite extensive studies, the mechanisms by which histone chaperones enable chromatin assembly remains elusive. Moreover, the global features of nucleosomes organized by histone chaperones are poorly understood. To address these problems, this work describes a unique single-molecule imaging technique named DNA curtain, which facilitates the investigation of the molecular details of nucleosome assembly by histone chaperones. DNA curtain is a hybrid technique that combines lipid fluidity, microfluidics, and total internal reflection fluorescence microscopy (TIRFM) to provide a universal platform for real-time imaging of diverse protein-DNA interactions.Using DNA curtain, the histone chaperone function of Abo1, the Schizosaccharomyces pombe bromodomain-containing AAA+ ATPase, is investigated, and the molecular mechanism underlying histone assembly of Abo1 is revealed. DNA curtain provides a unique approach for studying chromatin dynamics

Anomalous Light-Induced Charging in MoS2Monolayers with Cracks

© 2021 American Chemical Society.Monolayer MoS2 devices with Au electrodes were fabricated on SiO2/Si substrates with 50 nm high SiO2 nanopillar (NP) array patterns. In the NP patterns, many cracks were found in the MoS2 flakes, which were generated by the NP-induced mechanical strain during the wet transfer process. The cracks broke a few tens of micrometer MoS2 flakes, producing micrometer-sized flakes. Some of the small MoS2 flakes were suspended over the NPs, and others were not. The suspended flakes were highly strained, but the nonsuspended flakes were unstrained. Light-induced charging behaviors at the MoS2 flakes on the NPs were distinct from those on flat SiO2. More interestingly, positive and negative charging of an identical flake could be observed during repeated light on-and-off cycles. The strain-induced potential gradient in the MoS2 flakes on the NPs could cause exciton dissociation and charge migration under illumination, giving rise to light-induced charging. The polarity and amount of charges could be determined by the strain states and initial net charges of a specific flake and its neighboring flakes.11Nsciescopu

PWWP2B promotes DNA end resection and homologous recombination

Genome instability is one of the leading causes of gastric cancers. However, the mutational landscape of driver genes in gastric cancer is poorly understood. Here, we investigate somatic mutations in 25 Korean gastric adenocarcinoma patients using whole-exome sequencing and show that PWWP2B is one of the most frequently mutated genes. PWWP2B mutation correlates with lower cancer patient survival. We find that PWWP2B has a role in DNA double-strand break repair. As a nuclear protein, PWWP2B moves to sites of DNA damage through its interaction with UHRF1. Depletion of PWWP2B enhances cellular sensitivity to ionizing radiation (IR) and impairs IR-induced foci formation of RAD51. PWWP2B interacts with MRE11 and participates in homologous recombination via promoting DNA end-resection. Taken together, our data show that PWWP2B facilitates the recruitment of DNA repair machinery to sites of DNA damage and promotes HR-mediated DNA double-strand break repair. Impaired PWWP2B function might thus cause genome instability and promote gastric cancer development