Biology subjects

Ahola, T.

Publications and source records attributed to Ahola, T..

5 recordsLinked to original sources

bioRxiv2026

Metatranscriptomic Profiling of Viral Diversity in Aquatic Environments with a Focus on Microalgal Viruses

Freshwater microeukaryotes contribute to aquatic productivity, yet the RNA viruses associated with these communities remain incompletely characterized compared with their marine counterparts. Here, we used metatranscriptomics to profile viral diversity across five Finnish freshwater sites (one river and four lakes) and one coastal marine sample from Hiroshima Bay in the Seto Inland Sea, Japan. We recovered 399 viral operational taxonomic units (vOTUs), of which 285 (71.4%) represented RNA viruses distributed across five viral phyla and putatively associated with fungal, plant or algal, metazoan and bacterial hosts. DNA viruses formed a smaller component of the dataset, including bacteriophage-like vOTUs with transcripts encoding replication, structural, packaging, and lysis proteins. Two vOTUs, which were detected in the Vantaanjoki river sample, were putatively classified within the family Marnaviridae, which comprises RNA viruses that infect protists in marine and freshwater environments. Both vOTUs encoded conserved replication and picornavirus-like capsid domains, and one represented a near-complete dicistronic genome. RNA-dependent RNA polymerase (RdRp) -based phylogeny placed these vOTUs in a strongly supported lineage outside the currently recognized genera within the family Marnaviridae, supporting their provisional assignment to the candidate genus Vandarnavirus proposed here within Marnaviridae. Whole-genome comparisons using the IMG/VR v4 database revealed genetic similarities between the vOTUs representing the candidate Vandarnavirus genus and picorna-like virus sequences from freshwater, wetland, saltmarsh, and estuarine metatranscriptomes. These findings expand the known ecological range of marnavirus-like RNA viruses and identify freshwater habitats as under-sampled reservoirs of microalgae-associated viral sequences.

microbiology↗

bioRxiv2026

Discovery of dual thiobarbiturate-indole scaffold as a selective inhibitor targeting chikungunya virus nsP3 macrodomain through a cryptic binding pocket

The chikungunya virus (CHIKV) outbreak imposes a significant burden on healthcare systems and raises an urgent need for effective antiviral therapies. So far there are no specific drugs against CHIKV. A CHIKV macrodomain is critical for virulence and counteracts the host immune response, representing a promising antiviral drug target. Here, we describe small molecule inhibitors targeting the CHIKV macrodomain. Compound 1 (MDOLL-0273) was identified through a high-throughput screening using a fluorescence resonance energy transfer (FRET)-based assay, and its inhibitory activity was validated through multiple orthogonal assays. Compound 1 has a dual thiobarbiturate-indole scaffold and exhibits an IC50 of 8.9 {micro}M. X-ray crystallography revealed that the inhibitor occupies an adenine binding site of the macrodomain and extends into a novel cryptic pocket. Notably, the inhibitor shows high selectivity for the CHIKV macrodomain over a panel of human and viral ADP-ribosyl binding and hydrolyzing proteins. Structure-activity relationship studies and medicinal chemistry efforts provide a promising starting point for further hit optimization.

biochemistry↗

bioRxiv2026

Profiling of HeLa nucleoplasmic and nucleolar RNAs by Halo-seq proximity labeling

Subcellular RNA localization is a key regulator of gene expression, but transcriptome wide characterization of RNAs enriched in specific cellular compartments has been hindered by methodological limitations in throughput and spatial resolution. Halo-seq is an RNA proximity-labeling approach that enables the extraction of RNAs located near virtually any Halo-tagged bait protein. However, its broader application has been restricted by the limited availability of the required Halo ligand. Here we present a Halo-seq dataset profiling the nucleoplasmic and nucleolar transcriptomes of HeLa cells. Through experimental and computational validation, we demonstrate that our optimized Halo-seq protocol achieves high spatial specificity, enabling robust mapping of compartment-enriched RNA populations.

molecular biology↗

bioRxiv2026

dirCLIP profiles variant-specific RNA-protein interactions via nanopore long-read sequencing

RNA binding proteins (RBPs) control gene expression through their activities in essentially all processing steps of coding and noncoding RNAs and are dysregulated in disease. With >95% of human multi-exon genes undergoing alternative splicing, the inability to assign RBP sites to distinct RNA variants fundamentally limits our understanding of RNA regulation. We present dirCLIP, a method combining UV crosslinking and immunoprecipitation (CLIP) with amplification-free direct nanopore long-read sequencing preserving full-length transcripts. dirCLIP employs two complementary strategies: direct RNA sequencing detecting amino acid adduct-induced perturbations in current signals and direct cDNA sequencing capturing binding sites as mutations. Benchmarking dirCLIP with SRSF3 demonstrated >75% concordance with short-read-based data, revealed isoform-selective RNA binding and enabled detection of co-occurring binding sites in single RNA molecules. Application to the noncanonical RBP HMGA1 uncovered new AT-hook mediated RNA variant-specific interactions. dirCLIP fundamentally transforms our ability to interrogate RNA regulation of distinct isoforms and transcript variants with direct implications to disease mechanisms and development of RNA therapeutics.

molecular biology↗

bioRxiv2019

Separate domains of G3BP promote efficient clustering of alphavirus replication complexes and recruitment of the translation initiation machinery

G3BP-1 and -2 (hereafter referred to as G3BP) are multifunctional RNA-binding proteins involved in stress granule (SG) assembly. Viruses from diverse families target G3BP for recruitment to replication or transcription complexes in order to block SG assembly but also to acquire pro-viral effects via other unknown functions of G3BP. The Old World alphaviruses, including Semliki Forest virus (SFV) and chikungunya virus (CHIKV) recruit G3BP into viral replication complexes, via an interaction between FGDF motifs in the C-terminus of the viral non-structural protein 3 (nsP3) and the NTF2-like domain of G3BP. To study potential proviral roles of G3BP, we used human osteosarcoma (U2OS) cell lines lacking endogenous G3BP generated using CRISPR-Cas9 and reconstituted with a panel of G3BP1 mutants and truncation variants. While SFV replicated with varying efficiency in all cell lines, CHIKV could only replicate in cells expressing G3BP1 variants containing both the NTF2-like and the RGG domains. The ability of SFV to replicate in the absence of G3BP allowed us to study effects of different domains of the protein. We used immunoprecipitation to demonstrate that that both NTF2- like and RGG domains are necessary for the formation a complex between nsP3, G3BP1 and the 40S ribosomal subunit. Electron microscopy of SFV-infected cells revealed that formation of nsP3:G3BP1 complexes via the NTF2-like domain was necessary for clustering of cytopathic vacuoles (CPVs) and that the presence of the RGG domain was necessary for accumulation of electron dense material containing G3BP1 and nsP3 surrounding the CPV clusters. Clustered CPVs also exhibited localised high levels of translation of viral mRNAs as detected by ribopuromycylation staining. These data confirm that G3BP is a ribosomal binding protein and reveal that alphaviral nsP3 uses G3BP to concentrate viral replication complexes and to recruit the translation initiation machinery, promoting the efficient translation of viral mRNAs.

microbiology↗