Nuclear pores safeguard the integrity of the nuclear envelope.

Nuclear pore complexes (NPCs) mediate nucleocytoplasmic exchange, which is essential for eukaryotes. Mutations in the central scaffolding components of NPCs are associated with genetic diseases, but how they manifest only in specific tissues remains unclear. This is exemplified in Nup133-deficient mouse embryonic stem cells, which grow normally during pluripotency, but differentiate poorly into neurons.

Passage of the HIV capsid cracks the nuclear pore.

Upon infection, human immunodeficiency virus type 1 (HIV-1) releases its cone-shaped capsid into the cytoplasm of infected T cells and macrophages. The capsid enters the nuclear pore complex (NPC), driven by interactions with numerous phenylalanine-glycine (FG)-repeat nucleoporins (FG-Nups). Whether NPCs structurally adapt to capsid passage and whether capsids are modified during passage remains unknown, however.

Direct Capsid Labeling of Infectious HIV-1 by Genetic Code Expansion Allows Detection of Largely Complete Nuclear Capsids and Suggests Nuclear Entry of HIV-1 Complexes via Common Routes.

The cone-shaped mature HIV-1 capsid is the main orchestrator of early viral replication. After cytosolic entry, it transports the viral replication complex along microtubules toward the nucleus. While it was initially believed that the reverse transcribed genome is released from the capsid in the cytosol, recent observations indicate that a high amount of capsid protein (CA) remains associated with subviral complexes during import through the nuclear pore complex (NPC).

Nuclear Capsid Uncoating and Reverse Transcription of HIV-1.

After cell entry, human immunodeficiency virus type 1 (HIV-1) replication involves reverse transcription of the RNA genome, nuclear import of the subviral complex without nuclear envelope breakdown, and integration of the viral complementary DNA into the host genome. Here, we discuss recent evidence indicating that completion of reverse transcription and viral genome uncoating occur in the nucleus rather than in the cytoplasm, as previously thought, and suggest a testable model for nuclear import and uncoating. Multiple recent studies indicated that the cone-shaped capsid, which encases the genome and replication proteins, not only serves as a reaction container for reverse transcription and as a shield from innate immune sensors but also may constitute the elusive HIV-1 nuclear import factor.

Maturation of the matrix and viral membrane of HIV-1.

Gag, the primary structural protein of HIV-1, is recruited to the plasma membrane for virus assembly by its matrix (MA) domain. Gag is subsequently cleaved into its component domains, causing structural maturation to repurpose the virion for cell entry. We determined the structure and arrangement of MA within immature and mature HIV-1 through cryo-electron tomography.

HIV-1 uncoating by release of viral cDNA from capsid-like structures in the nucleus of infected cells.

HIV-1 replication commences inside the cone-shaped viral capsid, but timing, localization, and mechanism of uncoating are under debate. We adapted a strategy to visualize individual reverse-transcribed HIV-1 cDNA molecules and their association with viral and cellular proteins using fluorescence and correlative-light-and-electron-microscopy (CLEM). We specifically detected HIV-1 cDNA inside nuclei, but not in the cytoplasm.

Cone-shaped HIV-1 capsids are transported through intact nuclear pores.

Human immunodeficiency virus (HIV-1) remains a major health threat. Viral capsid uncoating and nuclear import of the viral genome are critical for productive infection. The size of the HIV-1 capsid is generally believed to exceed the diameter of the nuclear pore complex (NPC), indicating that capsid uncoating has to occur prior to nuclear import.

Structures and distributions of SARS-CoV-2 spike proteins on intact virions.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virions are surrounded by a lipid bilayer from which spike (S) protein trimers protrude. Heavily glycosylated S trimers bind to the angiotensin-converting enzyme 2 receptor and mediate entry of virions into target cells. S exhibits extensive conformational flexibility: it modulates exposure of its receptor-binding site and subsequently undergoes complete structural rearrangement to drive fusion of viral and cellular membranes.

Electric discharge evidence found in a new class of material in the Chicxulub ejecta.

Chicxulub impact (66 Ma) event resulted in deposition of spheroids and melt glass, followed by deposition of diamectite and carbonate ejecta represented by large polished striated rounded pebbles and cobbles, henceforth, called Albion Formation Pook's Pebbles, name given from the first site identified in central Belize, Cayo District. Here we report that magnetic analysis of the Pook's Pebbles samples revealed unique electric discharge signatures. Sectioning of Pook's Pebbles from the Chicxulub ejecta from the Albion Formation at Belize showed that different parts of Pook's Pebbles had not only contrasting magnetization directions, but also sharply different level of magnetizations.

Analysis of CA Content and CPSF6 Dependence of Early HIV-1 Replication Complexes in SupT1-R5 Cells.

HIV-1 infects host cells by fusion at the plasma membrane, leading to cytoplasmic entry of the viral capsid encasing the genome and replication machinery. The capsid eventually needs to disassemble, but time and location of uncoating are not fully characterized and may vary depending on the host cell. To study the fate of the capsid by fluorescence and superresolution (STED) microscopy, we established an experimental system that allows discrimination of subviral structures in the cytosol from intact virions at the plasma membrane or in endosomes without genetic modification of the virus.

Super-resolved insights into human immunodeficiency virus biology.

The recent development of fluorescence microscopy approaches overcoming the diffraction limit of light microscopy opened possibilities for studying small-scale cellular processes. The spatial resolution achieved by these novel techniques, together with the possibility to perform live-cell and multicolor imaging, make them ideally suited for visualization of native viruses and subviral structures within the complex environment of a host cell or organ, thus providing fundamentally new possibilities for investigating virus-cell interactions. Here, we review the use of super-resolution microscopy approaches to study virus-cell interactions, and discuss recent insights into human immunodeficiency virus biology obtained by exploiting these novel techniques.

Mouse Polyomavirus: Propagation, Purification, Quantification, and Storage.

Mouse polyomavirus (MPyV) is a member of the Polyomaviridae family, which comprises non-enveloped tumorigenic viruses infecting various vertebrates including humans and causing different pathogenic responses in the infected organisms. Despite the variations in host tropism and pathogenicity, the structure of the virions of these viruses is similar. The capsid, with icosahedral symmetry (ø, 45 nm, T = 7d), is composed of a shell of 72 capsomeres of structural proteins, arranged around the nucleocore containing approximately 5-kbp-long circular dsDNA in complex with cellular histones.

Involvement of microtubular network and its motors in productive endocytic trafficking of mouse polyomavirus.

Infection of non-enveloped polyomaviruses depends on an intact microtubular network. Here we focus on mouse polyomavirus (MPyV). We show that the dynamics of MPyV cytoplasmic transport reflects the characteristics of microtubular motor-driven transport with bi-directional saltatory movements.

Efficiency of cellular growth when creating small pockets of electric current along the walls of cells.

Pulses up to 11 Tesla magnetic fields may generate pockets of currents along the walls of cellular material and may interfere with the overall ability of cell division. We used prokaryotic cells (Escherichia coli) and eukaryotic cells (murine fibroblasts) and exposed them to magnetic pulses of intensities ranging from 1 millitesla (mT) to 11,000 mT. We found prokaryotic cells to be more sensitive to magnetic field pulses than eukaryotic cells.

Polyomavirus middle T-antigen is a transmembrane protein that binds signaling proteins in discrete subcellular membrane sites.

Murine polyomavirus middle T-antigen (MT) induces tumors by mimicking an activated growth factor receptor. An essential component of this action is a 22-amino-acid hydrophobic region close to the C terminus which locates MT to cell membranes. Here, we demonstrate that this sequence is a transmembrane domain (TMD) by showing that a hemagglutinin (HA) tag added to the MT C terminus is exposed on the outside of the cells, with the N terminus inside.

Minor capsid proteins of mouse polyomavirus are inducers of apoptosis when produced individually but are only moderate contributors to cell death during the late phase of viral infection.

Minor structural proteins of mouse polyomavirus (MPyV) are essential for virus infection. To study their properties and possible contributions to cell death induction, fusion variants of these proteins, created by linking enhanced green fluorescent protein (EGFP) to their C- or N-termini, were prepared and tested in the absence of other MPyV gene products, namely the tumor antigens and the major capsid protein, VP1. The minor proteins linked to EGFP at their C-terminus (VP2-EGFP, VP3-EGFP) were found to display properties similar to their nonfused, wild-type versions: they killed mouse 3T3 cells quickly when expressed individually.