Biology subjects

Pühringer, T.

Publications and source records attributed to Pühringer, T..

4 recordsLinked to original sources

bioRxiv2026

Structure of the Pre-Initiation Complex Explains CMGE Biogenesis

Summary paragraphWhen cells enter S phase, bidirectional DNA replication is initiated through the kinase-regulated recruitment of three activators (Cdc45, GINS and Pol epsilon) to a duplex DNA-loaded double hexamer of MCM ATPases. Together these proteins form two CMGE helicases that establish divergent replication forks as they become separated1. To understand CMGE biogenesis, we reconstituted the pre-Initiation Complex with purified yeast proteins. The cryo-EM structure shows a set of firing factors caught in the act of assembling two symmetric CMGEs. We show how stepwise complex formation reshapes MCM in preparation for DNA opening and we explain how ATP promotes firing-factor ejection and CMGE maturation. While we find that Sld2 promotes GINS recruitment to MCM as expected, it also aids efficient separation of the CMGE dimer, and it is essential for lagging strand ejection from MCM. These findings have direct implications for our understanding of the metazoan Sld2 ortholog, RECQL4, pointing to a replication-fork establishment mechanism conserved across eukaryotes.

biochemistry↗

bioRxiv2026

Mcm10 braces converging replicative helicases to pull apart origin DNA

Eukaryotic DNA replication initiation requires controlled, temporally separated steps to preserve genome stability. The MCM replicative helicase is loaded on duplex DNA as an inactive double hexamer, which nucleates the assembly of dimeric Cdc45-MCM-GINS-Pol epsilon (dCMGE) replisomes. Mcm10 splits dCMGE into two, generating divergent replication forks, but the mechanism is unknown. Using ATPase-defective yeast MCM variants that slow origin melting, we captured five reaction intermediates that explain the structural mechanism. Two Mcm10 molecules bridge across the CMGE dimer, bracing two converging helicases. The restrained MCM motors pull apart the two DNA filaments, such that each lagging strand becomes ejected through the Mcm2-5 gate. Our reconstituted structures resemble the double CMG stabilized by metazoan DONSON, pointing to an origin DNA melting mechanism conserved across evolution.

biochemistry↗

bioRxiv2024

MCM Double Hexamer Loading Visualised with Human Proteins

Eukaryotic DNA replication begins with the loading of the MCM replicative DNA helicase as a head-to-head double hexamer (DH) at origins of DNA replication1-3. Our current understanding of how DH is assembled by the Origin Recognition Complex (ORC), CDC6 and CDT1 comes mostly from budding yeast. Here we characterise human DH (hDH) loading using biochemical reconstitution and cryo-electron microscopy with purified proteins. We show that hDH engages DNA differently from yeast (yDH), and generates [~]5 base pairs of unwound DNA at the interface between hexamers, as seen in hDH isolated from cells4. We identify several differences from yeast in the order of factor recruitment and dependencies during hDH assembly. Unlike yeast5-8, the ORC6 subunit of ORC is not essential for initial MCM recruitment or hDH loading, but contributes to an alternative hDH assembly pathway requiring an intrinsically disordered region (IDR) in ORC1, which may work through a novel MCM-ORC (hMO*) intermediate. Our work presents a detailed view of how DHs are assembled in an organism utilising sequence-independent replication origins, it provides further evidence for diversity in eukaryotic DH assembly mechanisms9, and it represents the first step toward reconstitution of DNA replication initiation with purified human proteins.

biochemistry↗

bioRxiv2024

A molecular switch orchestrates the nuclear export of human messenger RNA

The nuclear export of messenger RNA (mRNA) is a key step in eukaryotic gene expression (Kohler and Hurt, 2007). Despite recent insights into the packaging of newly transcribed mRNAs into ribonucleoprotein complexes (mRNPs) (Pacheco-Fiallos et al., 2023; Bonneau et al., 2023), the subsequent events that govern mRNA export are poorly understood. Here, we elucidate the molecular basis of human mRNA export licensing, which involves the remodeling of mRNP-bound transcription-export complexes (TREX), the formation of export-competent mRNPs, the docking of mRNPs at the nuclear pore complex (NPC), and the release of mRNPs at the NPC to initiate export. Our biochemical and structural data uncover the ATPase DDX39/UAP56 as a central molecular switch that directs mRNPs through the TREX and the NPC-anchored TREX-2 complexes using its ATPase and mRNA-binding cycle. Collectively, these findings establish a mechanistic framework for a general and conserved mRNA export pathway.

molecular biology↗