Biology subjects

Jonas, S.

Publications and source records attributed to Jonas, S..

4 recordsLinked to original sources

bioRxiv2025

Active site assembly by SMG5 as a mechanism for SMG6 endonuclease licensing in nonsense-mediated mRNA decay

Nonsense-mediated mRNA decay (NMD) is a conserved eukaryotic surveillance pathway that eliminates transcripts containing premature termination codons (PTCs). While the recognition phase of NMD is well characterised, the effector step - how targeted mRNAs are nucleolytically degraded - remains incompletely understood. In metazoans, NMD employs an endonucleolytic route mediated by SMG6, a PIN-domain nuclease, alongside SMG5 and SMG7, which act downstream of PTC recognition. SMG5 has recently been proposed to license SMG6 activity, yet the molecular basis of this licensing has remained elusive. Here, we combine AlphaFold structural predictions with biochemical assays to investigate interactions among human SMG5, SMG6, and SMG7. Structural models predict a high-confidence interface between SMG5 and SMG6 PIN domains that forms a composite active site: a conserved SMG5 aspartate (D893) complements the SMG6 acidic triad to reinstate the canonical tetrad required for PIN-domain catalysis. In vitro, SMG6 alone exhibits weak endonucleolytic activity, which is enhanced [~]10-fold by SMG5 PIN. Mutational analyses confirm that conserved residues from both proteins are essential for this composite configuration. Our findings reveal that the SMG5 PIN domain, previously considered catalytically inert, plays a critical role in activating SMG6 by completing its active site. This work provides mechanistic insight into the SMG5-dependent licensing step and uncovers a composite PIN nuclease architecture at the heart of the metazoan NMD effector phase.

molecular biology↗

bioRxiv2024

Mechanistic basis of gene-specific transcription regulation by the Integrator complex

The Integrator complex (INT) regulates gene expression via premature transcription termination of RNA polymerase II (RNAP2) at promoter-proximal pausing sites. This attenuation of transcription is required for cellular response to external stimuli, cell differentiation and neurodevelopment. How gene-specific regulation is achieved by INT in an inducible manner remains unclear. Here, we identify two sites on INT subunits 13/14 that serve as direct binding hubs for diverse sets of sequence-specific transcription factors (TFs) and other transcription effector complexes. The TFs co-localize with INT genome-wide, increase INT abundance on target genes and co-regulate inducible transcriptional programs. Consistently, disruption of INT-TF contacts impairs sensory cilia formation in response to glucose starvation. Structural analysis places INTs TF binding hubs upstream of the transcription bubble when attached to paused RNAP2, consistent with simultaneous TF-promoter association. Our data establish TF-mediated recruitment of INT to promoters as a widespread mechanism for targeted and inducible transcription attenuation.

molecular biology↗

bioRxiv2022

Targeted high throughput mutagenesis of the human spliceosome reveals its in vivo operating principles

The spliceosome is a staggeringly complex machine comprising, in humans, 5 snRNAs and >150 proteins. We scaled haploid CRISPR-Cas9 base editing to target the entire human spliceosome and interrogated the mutants using the U2 snRNP/SF3b inhibitor, pladienolide B. Hypersensitive substitutions define functional sites in the U1/U2-containing A-complex but also in components that act as late as the second chemical step after SF3b is dissociated. Viable resistance substitutions map not only to the pladienolide B binding site but also to the G-patch (ATPase activator) domain of SUGP1, which lacks orthologs in yeast. We used these mutants and biochemical approaches to identify the spliceosomal disassemblase DHX15/hPrp43 as the ATPase ligand for SUGP1. These and other data support a model in which SUGP1 promotes splicing fidelity by triggering early spliceosome disassembly in response to kinetic blocks. Our approach provides a template for the analysis of essential cellular machines in humans.

molecular biology↗

bioRxiv2021

Biomolecular solid-state NMR spectroscopy at highest field: the gain in resolution at 1200 MHz

Progress in NMR in general and in biomolecular applications in particular is driven by increasing magnetic-field strengths leading to improved resolution and sensitivity of the NMR spectra. Recently, persistent superconducting magnets at a magnetic field strength (magnetic induction) of 28.2 T corresponding to 1200 MHz proton resonance frequency became commercially available. We present here a collection of high-field NMR spectra of a variety of proteins, including molecular machines, membrane proteins and viral capsids and others. We show this large panel in order to provide an overview over a range of representative systems under study, rather than a single best performing model system. We discuss both carbon-13 and proton-detected experiments, and show that in 13C spectra substantially higher numbers of peaks can be resolved compared to 850 MHz while for 1H spectra the most impressive increase in resolution is observed for aliphatic side-chain resonances.

biophysics↗