Hlavata, A. | Search bioRxiv

bioRxiv2025

Structure of cytoplasmic RNA polymerase II

RNA polymerase II (Pol II) must be assembled in the cytoplasm before it enters the nucleus, where it transcribes protein-coding genes. Although transcription by Pol II is intensively studied, how this central multi-subunit enzyme is made and the role of dedicated factors remains unclear. Here, we report the integrative structural analysis of a native human Pol II from the cytoplasm captured near the end of biogenesis. The complex contained Gdown1 and three biogenesis factors - RPAP2 and the critical small GTPases GPN1 and GPN3. Cryo-EM analysis of the complex revealed how Gdown1 and RPAP2 associate with Pol II and prevent the premature association of transcription factors. Further biochemical and cryo-EM analysis revealed how RPAP2 recruits GPN1-GPN3 to the complex, and how the assembly of the RPAP2-GPN1-GPN3 complex is controlled by GTP hydrolysis. The combined results uncover a network of interactions that chaperone cytoplasmic Pol II to prevent aberrant interactions, reveal a GTP-controlled switch during the final stages of Pol II biogenesis, and suggest a general mechanism for the action of GPN-loop GTPase family of enzymes.

biochemistry↗

bioRxiv2023

Role of Dynamin-Related Proteins 2 and SH3P2 in Clathrin-Mediated Endocytosis in Plants

Clathrin-mediated endocytosis (CME) is vital for the regulation of plant growth and development by controlling plasma membrane protein composition and cargo uptake. CME relies on the precise recruitment of regulators for vesicle maturation and release. Homologues of components of mammalian vesicle scission are strong candidates to be part of the scissin machinery in plants, but the precise roles of these proteins in this process is not fully understood. Here, we characterised the roles of Plant Dynamin-Related Proteins 2 (DRP2s) and SH3-domain containing protein 2 (SH3P2), the plant homologue to Dynamins recruiters, like Endophilin and Amphiphysin, in the CME by combining high-resolution imaging of endocytic events in vivo and characterisation of the purified proteins in vitro. Although DRP2s and SH3P2 arrive similarly late during CME and physically interact, genetic analysis of the Dsh3p1,2,3 triple-mutant and complementation assays with non-SH3P2-interacting DRP2 variants suggests that SH3P2 does not directly recruit DRP2s to the site of endocytosis. These observations imply that despite the presence of many well-conserved endocytic components, plants have acquired a distinct mechanism for CME. One Sentence SummaryIn contrast to predictions based on mammalian systems, plant Dynamin-related proteins 2 are recruited to the site of Clathrin-mediated endocytosis independently of BAR-SH3 proteins.

plant biology↗