Complex membrane remodeling during virion assembly of the 30,000 years-old Mollivirus sibericum

International audienceCellular membranes ensure functional compartmentalization by dynamic fusion-fission remodeling and are often targeted by viruses during entry, replication, assembly and egress. Nucleocytoplasmic large DNA viruses (NCLDVs) can recruit host-derived open membrane precursors to form their inner viral membrane. Using complementary 3D-electron microscopy techniques including focused-ion beam scanning electron microscopy and electron tomography, we show that the giant Mollivirus sibericum utilizes the same strategy but also displays unique features. Indeed, assembly is specifically triggered by an open cisterna with a flat pole in its center and open curling ends that grow by recruitment of vesicles, never reported for NCLDVs. These vesicles, abundant in the viral factory (VF), are initially closed but open once in close proximity to the open curling ends of the growing viral membrane. The flat pole appears to play a central role during the entire virus assembly process. While additional capsid layers are assembled from it, it also shapes the growing cisterna into immature crescent-like virions and is located opposite to the membrane elongation and closure sites, thereby providing virions with a polarity. In the VF, DNA-associated filaments are abundant and DNA is packed within virions, prior to particle closure. Altogether, our results highlight the complexity of the interaction between giant viruses and their host. Mollivirus assembly relies on the general strategy of vesicle recruitment, opening and shaping by capsid layers similar to all NCLDVs studied until now. However, the specific features of its assembly suggests that the molecular mechanisms for cellular membrane remodeling and persistence are unique.ImportanceSince the first giant virus Mimivirus was identified, other giant representatives are isolated regularly around the World and appear to be unique in several aspects. They belong to at least four viral families and the ways they interact with their hosts remain poorly understood. We focused on Mollivirus sibericum, the sole representative of "Molliviridae" which was isolated from a 30,000 years-old permafrost sample, and exhibits spherical virions of complex composition. In particular, we show that (i) assembly is initiated by a unique structure containing a flat pole positioned at the center of an open cisterna; (ii) core packing involves another cisterna-like element seemingly pushing core proteins into particles being assembled; (iii) specific filamentous structures contain the viral genome before packaging. Altogether, our findings increase our understanding on how complex giant viruses interact with their host and provide the foundation for future studies to elucidate the molecular mechanisms of Mollivirus assembly

Globalization and Mixing in the Visual Arts An Empirical Survey of 'High Culture' and Globalization

International audienceWhile there has been an increasing amount of research into globalization since the 1990s, empirical sociological studies in this area remain all too scarce. By analysing specific cases in contemporary visual art, this article shows that the widespread art world discourse on globalization, mixing and the abolition of borders is to a large extent based on illusion. By objectifying the positions occupied by different countries in the field of art, the article brings to light a marked hierarchy that reveals that, beyond the development of international exchanges, the art world still has a clearly defined centre comprising a small number of western countries, among which the US and Germany are pre-eminent, and a vast periphery, comprising all the other states. The specific example empirically analysed here leads to a reconsideration of earlier studies of cultural globalization, most of which are essentially abstract

Sulfolobus Spindle-Shaped Virus 1 Contains Glycosylated Capsid Proteins, a Cellular Chromatin Protein, and Host-Derived Lipids.

International audienceGeothermal and hypersaline environments are rich in virus-like particles, among which spindle-shaped morphotypes dominate. Currently, viruses with spindle- or lemon-shaped virions are exclusive to Archaea and belong to two distinct viral families. The larger of the two families, the Fuselloviridae, comprises tail-less, spindle-shaped viruses, which infect hosts from phylogenetically distant archaeal lineages. Sulfolobus spindle-shaped virus 1 (SSV1) is the best known member of the family and was one of the first hyperthermophilic archaeal viruses to be isolated. SSV1 is an attractive model for understanding virus-host interactions in Archaea; however, the constituents and architecture of SSV1 particles remain only partially characterized. Here, we have conducted an extensive biochemical characterization of highly purified SSV1 virions and identified four virus-encoded structural proteins, VP1 to VP4, as well as one DNA-binding protein of cellular origin. The virion proteins VP1, VP3, and VP4 undergo posttranslational modification by glycosylation, seemingly at multiple sites. VP1 is also proteolytically processed. In addition to the viral DNA-binding protein VP2, we show that viral particles contain the Sulfolobus solfataricus chromatin protein Sso7d. Finally, we provide evidence indicating that SSV1 virions contain glycerol dibiphytanyl glycerol tetraether (GDGT) lipids, resolving a long-standing debate on the presence of lipids within SSV1 virions. A comparison of the contents of lipids isolated from the virus and its host cell suggests that GDGTs are acquired by the virus in a selective manner from the host cytoplasmic membrane, likely during progeny egress.Although spindle-shaped viruses represent one of the most prominent viral groups in Archaea, structural data on their virion constituents and architecture still are scarce. The comprehensive biochemical characterization of the hyperthermophilic virus SSV1 presented here brings novel and significant insights into the organization and architecture of spindle-shaped virions. The obtained data permit the comparison between spindle-shaped viruses residing in widely different ecological niches, improving our understanding of the adaptation of viruses with unusual morphotypes to extreme environmental conditions

Global Markets and Contemporary Art

Today’s contemporary art world has to come to terms with a highly unstable socioeconomic context that is evolving rapidly and constantly, with the result that any analysis to establish the state of the demand and supply of artistic goods and services ina global scenario is quite complex. The supply of contemporary art is renewed and must continue to be renewed, in line with the recent requirements of demand and with economic and technological changes

Visual Artists’ Professional Situations and Trajectories. Between Institutions and the Market

International audienceSince the 19 th century and romanticism, the "singularity regime" (Nathalie Heinich)-which highlights the vocation and achievements of the individual creator-informs the artist figure. Recently, as if echoing this romantic imagery, the representation of the artist as an entrepreneur has been more and more put forward in the artistic sector itself, including in art schools and the creative industries. At the same time, the model of the artist as a worker (Pierre-Michel Menger), as part of competitive artistic fields (Pierre Bourdieu) and as embedded in collaborative "art worlds" (Howard Becker), stresses the competitive as well as the collective and collaborative dimension of artistic creation. Who exactly are visual artists in Switzerland today? What is or are the self-representation(s) of contemporary visual artists? What are their socio-demographic profiles-notably in terms of gender-and their link to professional or personal trajectories and positions? Do artists manage to live from their artistic production? To what extent are they integrated into the artistic market? And how do they define themselves? This contribution draws on a national inquiry with a quantitative online questionnaire on more than 450 artists in the visual field living and/ or working in Switzerland. The results outline the professional contours of today's visual artists, their novelties and permanencies, in a field structured by three poles-market logics, institutional support and non-integration. It highlights the strong role of the gender variable, as well as the dilemmas, contradictions and paradoxes that characterise todays artists' self-perception and condition