Search Results (557)

DNA damage requires repair via the endonuclease IV-mediated base excision repair (BER) pathway, which corrects apurinic/apyrimidinic (AP) sites. Chlamydophila pneumoniae AP endonuclease IV (CpEndoIV), the sole AP endonuclease in this pathogen, is crucial for genomic integrity. As humans lack a homologous protein, it represents a potential therapeutic target. In this study, we report the first crystal structure of CpEndoIV at 1.97 Å resolution. The structure reveals two Zn²⁺, one Mg²⁺, and a malonate molecule bound in the active site, marking the first observation of Mg²⁺ coordination in the EndoIV family. Compared to the three-Zn²⁺ model with a narrow, deep pocket for precise AP-site cleavage, the Zn²⁺/Mg²⁺-bound state has a wider, shallower pocket that might promote diverse catalytic activities. Combined with enzymatic assays, we suggest that the mixed Zn²⁺/Mg²⁺ model is better adapted for CpEndoIV to operate under host oxidative stress. Malonate binds to the metal ions, occupying the positions normally coordinated by water molecules. This binding mode may mimic the coordination of the substrate to the metal ions, and the protein conformation resembles that of the enzyme upon substrate binding at the active site. This study provides a structural basis for the functional characterization of CpEndoIV and offers a reference for the development of targeted inhibitors against diseases caused by Chlamydophila pneumoniae. Full article

Highly pathogenic avian influenza (HPAI) H5N1 clade 2.3.4.4b continues to circulate globally across wild birds, poultry, and an expanding range of mammalian hosts, highlighting the need for antiviral strategies that address the animal–environment–human interface. The influenza A polymerase acidic (PA) endonuclease, a key enzyme in viral transcription, represents a conserved antiviral target across host species. In this study, we present a computational prioritization framework integrating homology modeling, molecular docking, molecular dynamics simulations, and physicochemical filtering to identify candidate PA endonuclease inhibitors relevant to a One Health context. Homology models of contemporary H5N1 clade 2.3.4.4b PA sequences were constructed based on the crystallographic template 6FS8 and used for cross-host docking against a targeted ligand library. Docking analysis identified baloxavir, a reference inhibitor, and entecavir, a nucleoside analog, as compounds of interest, with entecavir demonstrating favorable binding behavior, particularly in the poultry-associated model. Molecular dynamics simulations of the poultry PA–entecavir complex indicated stable interaction over 170 ns, supported by low structural deviation and favorable binding free energy (ΔG ≈ −85 kJ/mol). Physicochemical profiling suggested that entecavir possesses properties such as high polarity and predicted aqueous solubility, which were considered within the translational filtering step of this computational workflow. However, these properties do not establish antiviral efficacy or practical suitability for field use. The study provides a structured framework for integrating cross-host structural analysis with basic translational considerations, supporting the identification of candidate compounds for further biochemical and virological evaluation within the context of H5N1 control. Full article

Norfloxacin has been widely found in water bodies and exhibits a strong toxic effect on aquatic organisms. To uncover its toxic mechanism on algae, the cell growth, reactive oxygen species (ROS) levels, physiological activities, mitochondrial membrane potential (MMP), caspase-3-like activity, cell morphology, TUNEL-positive nuclei and DNA ladders were determined in Chlamydomonas reinhardtii in exposure to norfloxacin. With raising norfloxacin concentration, the inhibitory and lethal effects on C. reinhardtii cells gradually enhanced, and the whole of the cells were dead under 50 μM for 24 h. During the cell death, respiratory and photosynthetic rate gradually reduced and disappeared after 24 h, while ROS quickly burst and maintained high levels during the 24 h. The MMP was markedly broken after 0.5 h, while caspase-3-like was activated, with the highest activity at the 2nd h. With prolonging the treatment time, the algal cells showed a gradual shrinking and wrinkling trend, while the numbers and fluorescence intensity of TUNEL-positive nuclei gradually increased. Meanwhile, the DNA was degraded by Ca²⁺-dependent endonucleases to show ladders after 6 h, and the degradation gradually enhanced during the death process. These characteristics demonstrate that norfloxacin can poison algae by triggering programmed cell death induced by the elevated ROS. Full article

Ustilago maydis is an economically significant biotrophic smut fungus, capable of infecting maize. This is a localized infection where tumors are formed, potentially in any of the aboveground parts of the plant. In extreme cases, maize plants may die. It is also dimorphic, i.e., it is capable of switching from yeast-like to filamentous forms. The switch can be induced by nitrogen sources, pH, and some lipids/oils. The active infectious form is the filamentous form which is capable of penetrating plant cells using the appressorium. This study focuses on understanding the mitochondrial genome diversity in U. maydis, the selection pressure on the genes encoded in the mitochondrial genome, and the phylogeny of the strains investigated. The results suggest that the strains maintained high consistency in genome architecture and synteny. The cox1 and cob genes in the genomes possessed different intron numbers, with the presence or absence of homing endonuclease genes (HEGs), which overall contributed to the differences in the genome sizes. Among the genes in the mitogenome, nad6 was the only gene that has a non-synonymous nucleotide change, but the overall changes within the mitogenomes suggest purifying selection. The study helped identify the different mitotypes using PCR, although further markers or whole-genome sequencing may be required to fully distinguish mitotypes. Full article

Group II introns are catalytic RNAs that combine self-splicing ribozyme activity with mobility and have played major roles in shaping organellar genome evolution. In green macroalgae of the genus Ulva, organellar genomes are highly compact, yet they harbor unusually diverse and dynamic repertoires of group II introns. To understand how organellar group II introns diversify and persist within compact organellar genomes, we performed a comparative analysis of mitochondrial and chloroplast group II introns across Ulva, integrating secondary structure reconstruction, intron occurrence patterns, and phylogenetic inference based on both conserved intron RNA regions and intron-encoded proteins (IEPs), including reverse transcriptase/maturase (RT/M) and LAGLIDADG homing endonuclease (LHE). A total of 168 mitochondrial and 123 chloroplast introns were identified and classified into 32 families belonging to seven major subgroups (IIA1-RT/M, IIA2-RT/M, IIB1-RT/M, IIB1-LHE, IIB2-RT/M, IIB2-LHE, and IIB-like). Most intron families retain the canonical six-domain architecture (DI–DVI), but four mitochondrial IIA families display a seven-domain configuration generated by the lineage-specific insertion of an additional stem-loop structure (DIIIa). Phylogenetic analyses revealed a high degree of congruence, supporting persistent coevolution between RNA scaffolds and their IEPs. Notably, the LHE-encoding families were scattered across distinct IIB lineages instead of forming a single clade, suggesting that at least two independent invasion events occurred within the IIB1 and IIB2 lineages. Analysis of intron occurrence frequency revealed an evolutionary continuum ranging from structurally intact and broadly distributed families to lineage-specific families exhibiting progressive scaffold degeneration, with the chloroplast infA-62 family representing a stably inherited lineage maintained through vertical transmission. These results suggest that organellar group II introns in Ulva evolve through coordinated scaffold remodeling, enzymatic replacement, and differential distribution patterns across genomic compartments, highlighting Ulva organellar genomes as a valuable comparative model for investigating the long-term evolution of mobile ribozymes within compact genomic environments. Full article

DNA cloning traditionally relies on two approaches: restriction endonuclease digestion-ligation, and homologous recombination involving exonucleases, polymerases, and other enzymes. Here, we present a novel cloning method that requires only restriction endonucleases, eliminating the need for exonucleases or polymerases. The linearized cloning vector and the foreign DNA fragment (FDF) containing overlapping sequences were mixed and incubated at the melting temperature of the overlapping DNA sequences for 5 min, then cooled slowly to 0 °C. The mixture was transformed into E. coli and positive transformants were obtained. This cloning method was named DNA ‘breathing’ recombination (DBR) cloning. The overlapping sequence between the linearized vector and the FDF is preferably from 12 to 16 base pairs. Even when the ends of the linearized vector contain mismatches of up to 20 base pairs with the ends of the FDF, the DBR cloning method can still proceed efficiently, enabling truly seamless assembly. Meanwhile, the DBR method supports one-step assembly of multiple fragments. Therefore, the DBR cloning method simplifies experimental operations and reduces experimental costs while maintaining high cloning efficiency. Full article

Eukaryotic DNA is wrapped around octamers of four core histones, forming nucleosomes. Histone post-translational modifications (PTMs) influence chromatin structure and the recruitment of regulatory factors, thereby affecting gene expression and DNA repair, including the response to DNA double-strand breaks (DSBs). Here, we describe a robust chromatin immunoprecipitation protocol combined with micrococcal nuclease digestion and DNA sequencing (MNase-ChIP-seq) to map histone modifications and their genome-wide distribution after the induction of a single DSB by the HO endonuclease in Saccharomyces cerevisiae. We validate the method by detecting changes in histone H3 methylation following HO transcriptional activation and DSB induction. This protocol enables reliable analysis of histone PTMs across mutant strains or stress conditions, supporting studies of chromatin dynamics in yeast. Full article

DNA double-strand breaks (DSBs) are primarily repaired in eukaryotic cells through two pathways: homologous recombination (HR) and non-homologous end joining (NHEJ). The thermotolerant yeast Kluyveromyces marxianus is recognized for its highly active NHEJ pathway, making it a suitable model organism for studying the role of NHEJ in DSB repair. To induce DSBs in K. marxianus DMKU3-1042, an expression cassette containing the gene encoding the endonuclease RsaI was integrated into the LYS1 locus of both the wild-type and NHEJ-deficient KU70 mutant strains. This cassette is regulated by the galactose-inducible promoter GAL10. Cells expressing RsaI and grown in galactose medium exhibited an elongated, rod-shaped morphology under a microscope. Following RsaI expression, the viability of transformed KU70 cells decreased during the first three hours of culture in liquid medium and then partially recovered after six hours of incubation. In contrast, the KU70 mutant cells failed to produce viable survivors. Pulsed-field gel electrophoresis analysis revealed distinct chromosomal separation patterns among various RsaI-transformed KU70 cells. These findings demonstrate that the repair of RsaI-induced DSBs in K. marxianus DMKU3-1042 results in new strains with several forms of rearranged chromosomes. Full article

Tissue decellularization aims to obtain bioscaffolds for regenerative applications by removing all cellular components while preserving the extracellular matrix (ECM) architecture. Although decellularization removes the majority of linear nuclear DNA (nDNA), residual amounts remain detectable. However, the fate of circular mitochondrial DNA (mtDNA) after decellularization has not yet been reported. Cell death or injury can cause the release of mtDNA, which is resistant to breakdown by exonucleases. Extracellular mtDNA acts as a damage-associated molecular pattern (DAMP) that can trigger immune responses. The aim of this study is to assess the presence of residual mtDNA in the liver, bile duct, and vascular scaffolds after decellularization and whether this causes inflammatory responses in macrophages. Decellularized tissues showed a marked reduction in total DNA content well below the threshold of 50 ng/mg tissue. However, in liver and vascular scaffolds, a relative increase in the mtDNA:nDNA ratio was detected in the remnant DNA fraction. Residual mtDNA in bioscaffolds acted as DAMPs causing macrophage activation, as shown by increased cell proliferation and cytokine production. Strategies to further reduce remnant mtDNA were tested. We found that treatment with the endonuclease enzyme HpaII was effective in degrading residual mtDNA. Importantly, mtDNA removal resulted in a significantly reduced macrophage activation. In conclusion, our study shows that mtDNA is relatively resistant to the decellularization procedure and can act as a DAMP in bioscaffolds. This underscores the importance of removing mtDNA from decellularized bioscaffolds to improve the immunocompatibility for biomedical applications. Full article

Restriction–modification (RM) systems contribute to genome plasticity in Mycoplasma hominis, a facultative pathogen with an extremely small but highly heterogeneous genome. The MhoVII RM system, which contains a fusion of two methyltransferases (MTases), M1 and M2, was recently identified within a family of Type II RM systems, but its specificity and biological function remained unknown. Phylogenetic analysis revealed that M1 and M2 belong to distinct MTase classes clustering within the YhdJ and MTaseD12 branches, respectively. In this study, the dissemination, expression and function of the MhoVII system was analyzed in detail using Oxford Nanopore-based methylation analysis, recombinant expression of the individual RM components in Escherichia coli, and methylation-sensitive restriction assays. It was thus possible to demonstrate that M1 and M2 methylate the complementary non-palindromic motifs GATG and CATC, and that the associated restriction endonuclease cleaves only DNA lacking 6mA methylation at these sites. The transcriptional analysis of mid-to-late logarithmic cultures indicated a polycistronic organization of the MhoVII genes, and GATG/CATC-driven methylation analysis revealed culture-dependent methylation differences, suggesting a post-transcriptional regulation, whereas in the infection of HeLa cells, MhoVII transcription was highest at the beginning and was then gradually downregulated in the later stages of infection. These findings establish MhoVII as a previously uncharacterized Type II RM system. Full article

The modified DNA base 2,6 aminopurine (2-aminoadenine, (d)Z base) was originally found in phages to counteract host-encoded restriction systems. However, only a limited number of restriction endonucleases (REases) have been tested on dZ-modified DNA. Here, we report the activity results of 147 REases on dZ-modified PCR DNA. Among the enzymes tested, 53% are resistant or partially resistant, and 47% are sensitive when their restriction sites contain one to six modified bases. Sites with four to six dZ substitutions are most likely to resist Type II restriction. Our results support the notion that dZ-modified phage genomes evolved to combat host-encoded restriction systems. dZ-modified DNA can also reduce phage T5 exonuclease degradation, but has no effect on RecBCD digestion. When two genes for dZ biosynthesis and one gene for dATP hydrolysis from Salmonella phage PMBT28 (purZ (adenylosuccinate synthetase), datZ (dATP triphosphohydrolase), and mazZ ((d)GTP-specific diphosphohydrolase) were cloned into an E. coli plasmid, the level of dZ incorporation reached 19–20% of adenosine positions. dZ levels further increased to 29–44% with co-expression of a DNA polymerase gene from the same phage. High levels of dZ incorporation in recombinant plasmid are possible by co-expression of purZ, mazZ, datZ and phage DNA helicase, dpoZ (DNA polymerase) and ssb (single-stranded DNA binding protein SSB). This work expands our understanding of the dZ modification of DNA and opens new avenues for engineering restriction systems and therapeutic applications. Full article

Plant RNA interference (RNAi) is a fundamental antiviral defense that relies on coordinated activities of DICER-like endonucleases (DCLs), Argonaute proteins (AGOs) and RNA-dependent RNA polymerases (RDRs). Over the past decades, studies using model and crop species have uncovered complex and often redundant roles for DCLs and RDRs in generating and amplifying virus-derived small interfering RNAs (vsiRNAs), in addition to connections with transcriptional gene silencing (TGS) and epigenetic defenses against DNA viruses. Concurrently, plant viruses have evolved diverse counterstrategies—proteinaceous RNA silencing suppressors (RSSs), exoribonuclease (XRN)-resistant noncoding RNAs, and indirect manipulation of host pathways—to evade RNAi. Driven by the co-evolutionary arms race, plants have developed sophisticated counter-countermeasures that modulate or overcome viral anti-RNAi activity. Accumulated evidence suggests that plants encode host factor genes that are activated to degrade or sequester viral components such as RSSs against viral infection. On the other hand, plants have also evolved endogenous host modulators of antiviral RNAi that can either reinforce the antiviral response or be co-opted by viruses to antagonize it, representing a furious dynamic molecular battling mechanism. Here, we review recent advances in the molecular functions of DCLs and RDRs across species, summarize newly discovered viral counter-defenses (including RNA-based suppressors), and discuss host counter-countermeasures. We research key areas—such as the roles of RDRγ-class proteins, RTL1 (RNase three-like 1)-mediated competition with DCLs, and the mechanistic impact of viral noncoding RNAs—and outline translational opportunities for improving virus resistance in crops through breeding, biotechnological approaches, and RNA-based applications. Full article

Mitochondrial genomes play a central role in fungal physiology and adaptation, yet their evolutionary dynamics during domestication remain poorly understood. Here, we performed a comparative mitogenomic and gene-expression analysis of three Pleurotus ostreatus dikaryotic strains differing in origin and degree of adaptation to laboratory conditions: the long-term commercial strain dkN001, the laboratory-maintained wild isolate dkF515, and the recently collected wild strain dkN009. High-throughput Illumina sequencing enabled complete assembly of circular mitochondrial genomes, revealing substantial size variation among strains, where the dkN001 strain exhibited the second smallest mitogenome reported for the genus Pleurotus. Comparative analyses showed >99% sequence identity between wild isolates and ~95% identity relative to the commercial strain. Variations in genome size among strains were associated with intron dynamics in the cox1 and rnl genes, as well as intron loss predominantly in the commercial strain dkN001, consistent with mitochondrial genome streamlining during domestication. Expression profiling of mitochondrial protein-coding genes (PCGs) under multiple culture conditions revealed conserved transcriptional responses in dkN001 and dkF515 that contrasted sharply with those of dkN009. The differences observed, which affected components of the electron transport chain, suggested shifts in energy metabolism associated with long-term laboratory maintenance. Therefore, our results demonstrate that domestication in P. ostreatus involves both structural remodelling of the mitogenome and changes in regulation of mitochondrial PCGs, highlighting the importance of mitonuclear interactions in fungal adaptation to controlled environments. Full article

Bacterial and viral diseases significantly reduce soybean (Glycine max) yield and quality. RNA modifications, particularly N⁶-methyladenosine (m⁶A), are increasingly recognized as having a regulatory role in plant–pathogen interactions, but the m⁶A methylome of soybean during viral and bacterial infection has not yet been characterized. Here, we performed transcriptome sequencing and MeRIP-seq (methylated RNA immunoprecipitation followed by high-throughput sequencing) of soybean leaves infected with Soybean mosaic virus (SMV) and/or Pseudomonas syringae pv. glycinea (Psg). In general, m⁶A peaks were highly enriched near stop codons and in 3′-UTR regions of soybean transcripts, and m⁶A methylation was negatively correlated with transcript abundance. Multiple genes showed differential methylation between infected and control plants: 1122 in Psg-infected plants, 539 in SMV-infected plants, and 2269 in co-infected plants; 195 (Psg), 84 (SMV), and 354 (Psg + SMV) of these transcripts were both differentially methylated and differentially expressed. Interestingly, viral infection was predominantly associated with hypermethylation and downregulation, whereas bacterial infection was predominantly associated with hypomethylation and upregulation. GO and KEGG enrichment analysis revealed shared processes likely affected by changes in m⁶A methylation during bacterial and viral infection, including ATP-dependent RNA helicase activity, RNA binding, and endonuclease activity, as well as specific processes affected by only one pathogen. Our findings shed light on the role of m⁶A modifications during pathogen infection and highlight potential targets for epigenetic editing to increase the broad-spectrum disease resistance of soybean. Full article

Factor V (FV) Leiden and F2 G20210A are inherited genetic risk factors that are in the first line of laboratory tests for thromboembolic diseases. Their detection relies on PCR assays, which are subject to contamination, as well as pipetting error, when manually performed and require individual assays for each gene. In this article, we report an improved PCR and restriction endonuclease assay for the simultaneous detection of the FV Leiden and F2 G20210A variants, based on multiplex amplification with fluorescent primers, digestion control, identity monitoring, and contamination tracking. Full article