Biology subjects

Williams, J. G.

Publications and source records attributed to Williams, J. G..

12 recordsLinked to original sources

bioRxiv2026

Molecular architecture and assembly of the human RNA Degradosome

The PNPase exoribonuclease interacts with the SUV3 helicase to form the human RNA Degradosome responsible for processive mitochondrial RNA turnover and quality control. Although structural data reveals the trimeric PNPase architecture along with the monomeric and dimeric states of SUV3, the molecular basis of their assembly for processive RNA degradation remains poorly understood. Here we present the molecular characterization of the human RNA Degradosome and define critical molecular features that regulate complex formation. We identify the protein regions required for RNA Degradosome formation and establish the minimum components necessary for the SUV3-PNPase interaction. Chemical crosslinking mass spectrometry analysis reveals distance restraints that position the SUV3 N-terminal domain alongside of the PNPase S1 domain, defining an important interface for complex formation. These findings provide mechanistic insight into how PNPase and SUV3 assemble to form the human RNA Degradosome.

biochemistry↗

bioRxiv2026

Short-term methionine starvation induces de novo diurnal oscillations of hepatic m6A RNA methylation

Dietary methionine restriction has been shown to improve metabolic health and treat multiple diseases. Methionine metabolism regulates transmethylation reactions, including N6-methyladenosine (m6A) RNA methylation, by modulating the availability of S-adenosyl methionine (SAM). Both m6A RNA methylation and methionine metabolism are involved in the regulation of the circadian clock. However, it remains unclear whether dietary methionine influences circadian rhythms through the regulation of m6A RNA modification. In this study, we investigated the effects of short-term methionine deprivation on the diurnal oscillations of m6A RNA methylation in the mouse liver. We found that a methionine-deficient (MD) diet reprogrammed the cyclic expression patterns of m6A writers, erasers, and readers. Methylated RNA immunoprecipitation sequencing (MeRIP-seq) revealed that the MD diet induced de novo diurnal m6A oscillations in genes associated with RNA processing, protein translation, protein ubiquitination, and mTORC1 signaling pathways. RNA-seq and quantitative proteomics analyses demonstrated that MD-induced changes in m6A RNA levels were linked to alterations in mRNA and protein abundance. We observed that dynamic m6A RNA methylation of the transcripts encoding two key enzymes, MAT2A and CBS, helps maintain methionine homeostasis in response to methionine starvation. These findings identify m6A RNA methylation as a key mechanism linking methionine metabolism to circadian regulation.

molecular biology↗

bioRxiv2026

CNOT10 is involved in TTP-mediated AU-rich element containing mRNA metabolism, independent of mRNA decay regulation

Tristetraprolin (TTP)/ ZFP36 is an RNA binding protein that is involved in the turnover regulation of target adenylate-uridylate-rich RNA element (ARE) containing mRNAs. AREs are present in the 3-untranslated region of transcripts expressed from many immediate-early genes, including cytokines and chemokines. It has been demonstrated that TTP-mediated post-transcriptional mRNA decay regulation is crucial for modulating physiological control, particularly in response to inflammatory stimulation. TTP is associated with the CCR4-NOT deadenylation complex through the TTP C-terminus to promote mRNA decay. However, it is not fully understood whether there are additional sites within TTP that contribute to its function through interacting with other factors. We analyzed the functionality of the unique tryptophan residues located in the TTP N-terminus using a cell-based assay system that consists of a tetracycline-responsive CMV promoter-driven, intron-inserted luciferase (LUC). This system enabled us to analyze TTP activity during both the early phase and the steady-state phase of gene expression, as well as in the post-transcriptional mRNA decay following the treatment of tetracycline analogs. Meanwhile, we identified putative TTP associates using a proximity labeling method. We found that tryptophan residues in the TTP N-terminus together with CNOT10, a component of the CCR4-NOT complex, were involved specifically in the reduction of the ARE-containing LUC mRNA level during the early phase of gene expression. However, they were not involved in the decay of LUC mRNA in the steady-state phase. We propose a novel post-transcriptional TTP functionality in the reduction of ARE-containing mRNA level, which differs from the well-characterized mRNA decay activity.

molecular biology↗

bioRxiv2025

Human Pumilio proteins use fuzzy multivalent hydrophobic interactions to recruit the CCR4-NOT deadenylase complex to repress mRNAs

Pumilio (PUM) proteins are conserved RNA-binding proteins that control mRNAs involved in development, proliferation, and stem cell differentiation. Human PUM1 and PUM2 repress targets by recruiting the CCR4-NOT deadenylase complex through a metazoan-specific N-terminal repression domain (RD3), which is predicted to be intrinsically disordered. Here we dissect RD3 using cell-based reporter assays, protein interaction assays with recombinant proteins, and crosslinking mass spectrometry. We identify multiple short RD3 peptides that are sufficient for repression and bind directly to the C-terminal NOT module of CCR4-NOT, comprising CNOT1, CNOT2, and CNOT3 subunits. Crosslinking reveals numerous mutually exclusive contacts between RD3 and the NOT module, consistent with a multivalent "fuzzy" binding mode in which interactions are not defined by a single sequence or structure. Sequence scrambling shows that the linear amino acid order of RD3 is dispensable, whereas its physicochemical composition, in particular distributed aliphatic and aromatic residues, is essential for repression and CCR4-NOT binding. These findings support a model in which low-affinity, multivalent interactions between intrinsically disordered regions (IDRs) and effector complexes, governed by amino acid composition rather than precise sequence, underlie robust PUM-mediated repression, and exemplify general principles by which IDRs recruit the CCR4-NOT complex to regulate gene expression. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=74 SRC="FIGDIR/small/695197v1_ufig1.gif" ALT="Figure 1"> View larger version (18K): org.highwire.dtl.DTLVardef@d4680aorg.highwire.dtl.DTLVardef@fa9c3dorg.highwire.dtl.DTLVardef@12783f7org.highwire.dtl.DTLVardef@148e657_HPS_FORMAT_FIGEXP M_FIG Graphical Abstract C_FIG

molecular biology↗

bioRxiv2025

The DND1-NANOS3 complex shapes the primordial germ cell transcriptome via a heptanucleotide sequence in mRNA 3'UTRs

The RNA-binding proteins DND1 and NANOS3 are essential for primordial germ cell survival1-5. Their co-immunoprecipitation and overlapping loss-of-function phenotypes suggest joint function6-8, yet how they co-regulate target mRNAs remains unclear. Here, we developed Tandem PAR-CLIP and identified a DND1-NANOS3 ribonucleoprotein that specifically recognizes an AUGAAUU heptanucleotide on target mRNAs, termed the NANOS3-dependent DND1 Recognition Element (N3-DRE). mRNAs containing 3'-UTR N3-DREs are aberrantly upregulated in DND1- or NANOS3-deficient germ cells and encode key cell-cycle and epigenome regulators, such as CDK1. Genome editing showed that the N3-DRE is essential for Cdk1 repression in mouse PGCs in vivo. A 1.7-[A] crystal structure of the ternary complex of DND1, NANOS3, and CDK1- N3-DRE RNA revealed a continuous RNA-binding surface that confers high-affinity, sequence- specific recognition. Together, these findings define the molecular and functional basis of N3-DRE-mediated mRNA regulation in germ cell development. Moreover, we provide a paradigm of two RNA-binding proteins with low (DND1) or no (NANOS3) intrinsic sequence-specificity, jointly building a high-information-content RNA sequence motif that is different from the sum of their individual preferences. Because RNA-binding protein specificities are typically studied individually9-13, rather than in the context of ribonucleoproteins, this type of "two-factor authorization" may be an underappreciated mechanism to protect posttranscriptional gene regulatory networks from aberrant expression of an individual ribonucleoprotein component.

molecular biology↗

bioRxiv2023

Effects of oscillation phase on discrimination performance in a visual tilt illusion

Neural oscillations reflect fluctuations in the relative excitation/inhibition of neural systems1-5 and are theorised to play a critical role in several canonical neural computations6-9 and cognitive processes10-14. These theories have been supported by findings that detection of visual stimuli fluctuates with the phase of oscillations at the time of stimulus onset15-23. However, null results have emerged in studies seeking to demonstrate these effects in visual discrimination tasks24-27, raising questions about the generalisability of these phenomena to wider neural processes. Recently, we suggested that methodological limitations may mask effects of oscillation phase in higher-level sensory processing28. Thus, to test the generality of phasic influences requires a task that requires stimulus discrimination but depends on early sensory processing. Here, we examined the influence of oscillation phase in the visual tilt illusion, in which an oriented centre grating is perceived titled away from the orientation of a surround grating29. This illusion is produced by lateral inhibitory interactions in early visual processing30-32. We presented centre gratings at participants titrated subjective vertical angle and had participants report whether the grating appeared tilted leftward or rightward of vertical on each trial while measuring their brain activity with EEG. We observed a robust fluctuation in orientation perception across different phases of posterior alpha and theta oscillations, consistent with fluctuating illusion magnitude across the oscillatory cycle. These results confirm that oscillation phase affects complex processing involved in stimulus discrimination, consistent with their purported role in canonical computations that underpin cognition.

neuroscience↗

bioRxiv2022

Structural Basis for pre-tRNA Recognition and Processing by the Human tRNA Splicing Endonuclease Complex

Across all walks of life, certain transfer RNA (tRNA) transcripts contain introns. Pre-tRNAs with introns require splicing to form the mature anticodon stem loop (ASL). In eukaryotes, tRNA splicing is initiated by the heterotetrameric tRNA splicing endonuclease (TSEN) complex. All TSEN subunits are essential and mutations within the complex are associated with a family of neurodevelopmental disorders known as pontocerebellar hypoplasia (PCH). The pathogenesis of PCH is poorly understood. Moreover, a lack of structures for any eukaryotic TSEN complex has hindered our understanding of tRNA recognition and processing. Here, we report Cryo-Electron Microscopy (cryo-EM) structures of the human TSEN*pre-tRNA complex, trapped in the pre-cleavage state, at near atomic resolution. These structures reveal the overall architecture of the complex, along with extensive tRNA binding interfaces within the complex. Although it shares structural homology with archaeal TSENs, the human TSEN complex contains additional features important for recognizing the acceptor stem and D-arm of the pre-tRNA. Our findings also establish the TSEN54 subunit as more than a simple molecular ruler; it functions as a pivotal scaffold for the pre-tRNA and the two endonuclease subunits, TSEN2 and TSEN34. Finally, the human TSEN structures enable detailed visualization of the molecular environments of PCH-causing missense mutations, providing crucial insight into the mechanism of eukaryotic pre-tRNA splicing and neurodevelopmental disease.

biochemistry↗

bioRxiv2021

Characterization of SARS2 Nsp15 Nuclease Activity Reveals it's Mad About U

Nsp15 is a uridine specific endoribonuclease that coronaviruses employ to cleave viral RNA and evade host immune defense systems. Previous structures of Nsp15 from across Coronaviridae revealed that Nsp15 assembles into a homo-hexamer and has a conserved active site similar to RNase A. Beyond a preference for cleaving RNA 3 of uridines, it is unknown if Nsp15 has any additional substrate preferences. Here we used cryo-EM to capture structures of Nsp15 bound to RNA in pre- and post-cleavage states. The structures along with molecular dynamics and biochemical assays revealed critical residues involved in substrate specificity, nuclease activity, and oligomerization. Moreover, we determined how the sequence of the RNA substrate dictates cleavage and found that outside of polyU tracts, Nsp15 has a strong preference for purines 3 of the cleaved uridine. This work advances our understanding of how Nsp15 recognizes and processes viral RNA and will aid in the development of new anti-viral therapeutics.

biochemistry↗

bioRxiv2020

Cryo-EM Structures of the SARS-CoV-2 Endoribonuclease Nsp15

New therapeutics are urgently needed to inhibit SARS-CoV-2, the virus responsible for the on-going Covid-19 pandemic. Nsp15, a uridine-specific endoribonuclease found in all coronaviruses, processes viral RNA to evade detection by RNA-activated host defense systems, making it a promising drug target. Previous work with SARS-CoV-1 established that Nsp15 is active as a hexamer, yet how Nsp15 recognizes and processes viral RNA remains unknown. Here we report a series of cryo-EM reconstructions of SARS-CoV-2 Nsp15. The UTP-bound cryo-EM reconstruction at 3.36 [A] resolution provides molecular details into how critical residues within the Nsp15 active site recognize uridine and facilitate catalysis of the phosphodiester bond, whereas the apo-states reveal active site conformational heterogeneity. We further demonstrate the specificity and mechanism of nuclease activity by analyzing Nsp15 products using mass spectrometry. Collectively, these findings advance understanding of how Nsp15 processes viral RNA and provide a structural framework for the development of new therapeutics.

biochemistry↗

bioRxiv2020

Streptococcus pyogenes M1T1 variants induce an inflammatory phenotype in neutrophils

Invasive infections due to Group A Streptococcus (GAS) advance rapidly causing tissue degradation and unregulated inflammation. Neutrophils are the primary immune cells that respond to GAS. The neutrophil response to GAS was characterised in response to two M1T1 isolates; 5448 and animal passaged variant 5448AP. Neutrophil co-incubation with 5448AP allowed proliferation of GAS while it also lowered the production of reactive oxygen species by neutrophils when compared with 5448. Infection with both strains invoked neutrophil death, however apoptosis was reduced in response to 5448AP. Both strains induced neutrophil caspase-1 activation and caspase-4 expression in vitro, with caspase-1 activation detected in vivo. Thus, GAS infection of neutrophils corresponds to increased caspase-1 activity and caspase-4 expression, consistent with inflammasome activation and pyroptosis. GAS infections that promote an inflammatory neutrophil phenotype may contribute to increased inflammation yet ineffective bacterial eradication, contributing to the speed and severity of invasive GAS infections.

microbiology↗

bioRxiv2019

It takes two (Las1 HEPN Endoribonuclease Motifs) to cut the RNA right

Las1 is an essential endoribonuclease that is well-conserved across eukaryotes and a newly established member of the HEPN (higher eukaryotes and prokaryotes nucleotide-binding) nuclease family. HEPN nucleases participate in diverse RNA cleavage pathways and share a short HEPN nuclease motif important for RNA cleavage. While most HEPN nucleases participate in stress activated RNA cleavage pathways, Las1 plays a fundamental role in processing the pre-ribosomal RNA. Underscoring the significance of Las1 function, mutations to the LAS1L gene have been associated with neurological dysfunction. Two juxtaposed Las1 HEPN nuclease motifs create its composite nuclease active site, however the roles of the individual HEPN residues are poorly defined. Here we show through a combination of in vivo and in vitro studies that both Las1 HEPN nuclease motifs are required for nuclease activity and fidelity. Through in-depth sequence analysis and systematic mutagenesis, we define the consensus Las1 HEPN nuclease motif and uncover its canonical and specialized elements. Using reconstituted Las1 HEPN-HEPNchimeras, we define the molecular requirements for RNA cleavage. Intriguingly, both copies of the Las1 HEPN motif are necessary for nuclease specificity revealing that both HEPN motifs participate in coordinating the RNA within the active site. Taken together, our work reveals critical information about HEPN nuclease function and establishes that HEPN nucleases can be re-wired to cleave alternative RNA substrates.

molecular biology↗

bioRxiv2018

Bacteria boost mammalian host NAD metabolism by engaging the deamidated biosynthesis pathway

Nicotinamide adenine dinucleotide (NAD), a cofactor for hundreds of metabolic reactions in all cell types, plays an essential role in diverse cellular processes including metabolism, DNA repair, and aging 1. NAD metabolism is critical to maintain cellular homeostasis in response to the environment, and disruption of this homeostasis is associated with decreased cellular NAD levels in aging 2. Conversely, elevated NAD synthesis is required to sustain the increased metabolic rate of cancer cells 3,4. Consequently, therapeutic strategies aimed to both upregulate NAD (i.e. NAD-boosting nutriceuticals) or downregulate NAD (inhibitors of key NAD synthesis enzymes) are being actively investigated 5-10. However, how this essential metabolic pathway is impacted by the environment remains unclear. Here, we report an unexpected trans-kingdom cooperation between bacteria and mammalian cells wherein bacteria contribute to host NAD biosynthesis. Bacteria confer cancer cells with the resistance to inhibitors of NAMPT, the rate limiting enzyme in the main vertebrate NAD salvage pathway. Mechanistically, a microbial nicotinamidase (PncA) that converts nicotinamide to nicotinic acid, a key precursor in the alternative deamidated NAD salvage pathway, is necessary and sufficient for this protective effect. This bacteria-enabled resistance mechanism that allows the mammalian host to bypass the drug-induced metabolic block represents a novel paradigm in drug resistance. This host-microbe metabolic interaction also enables bacteria to dramatically enhance the NAD-boosting efficiency of nicotinamide supplementation in vitro and in vivo, demonstrating a crucial role of microbes, gut microbiota in particular, in organismal NAD metabolism.

biochemistry↗