Sapoviruses are one of the major agents of acute gastroenteritis in childhood. They form a tight genetic cluster (genus) in the Caliciviridae family that regroups both animal and human pathogenic strains. No permissive tissue culture has been developed for human sapovirus, limiting its characterization to surrogate systems. We report here on the first extensive characterization of the key enzyme of replication, the RNAdependent RNA polymerase (RdRp) pol synthesizes a double-stranded RNA or labels the template 3 terminus by terminal transferase activity. Initiation of RNA synthesis occurs de novo on heteropolymeric templates or in a primerdependent manner on polyadenylated templates. Strikingly, this mode of initiation of RNA synthesis was also described for norovirus, but not for lagovirus, suggesting structural and functional homologies in the RNAdependent RNA polymerase of human pathogenic caliciviruses. This first experimental evidence makes sapovirus 3D pol an attractive target for developing drugs to control calicivirus infection in humans.

Molecular dynamics simulations of native α-, β-, and γ-cyclodextrin in aqueous solution have been conducted with the goal to investigate the performance of the CHARMM36 force field, the AMBER-compatible q4md-CD force field, and five variants of the GROMOS force field. The properties analyzed are structural parameters derived from X-ray diffraction and NMR experiments as well as hydrogen bonds and hydration patterns, including hydration free enthalpies. Recent revisions of the torsional-angle parameters for carbohydrate systems within the GROMOS family of force fields lead to a significant improvement of the agreement between simulated and experimental NMR data. Therefore, we recommend using the variant 53A6 instead of 53A6 and 56A6 or 2016H66 instead of 56A6 to simulate cyclodextrins in solution. The CHARMM36 and q4md-CD force fields show a similar performance as the three recommended GROMOS parameter sets. A significant difference is the more flexible nature of the cyclodextrins modeled with the CHARMM36 and q4md-CD force fields compared to the three recommended GROMOS parameter sets.

Caliciviridae are human or non-human pathogenic viruses with a high diversity. Some members of the Caliciviridae, i.e. human pathogenic norovirus or rabbit hemorrhagic disease virus (RHDV), are worldwide emerging pathogens. The norovirus is the major cause of viral gastroenteritis worldwide, accounting for about 85% of the outbreaks in Europe between 1995 and 2000. In the United States, 25 million cases of infection are reported each year. Since its emergence in 1984 as an agent of fatal hemorrhagic diseases in rabbits, RHDV has killed millions of rabbits and has been dispersed to all of the inhabitable continents. In view of their successful and apparently increasing emergence, the development of antiviral strategies to control infections due to these viral pathogens has now become an important issue in medicine and veterinary medicine. Antiviral strategies have to be based on an understanding of the epidemiology, transmission, clinical symptoms, viral replication and immunity to infection resulting from infection by these viruses. Here, we provide an overview of the mechanisms underlying calicivirus infection, focusing on the molecular aspects of replication in the host cell. Recent experimental data generated through an international collaboration on structural biology, virology and drug design within the European consortium VIZIER is also presented. Based on this analysis, we propose antiviral strategies that may significantly impact on the epidemiological characteristics of these highly successful viral pathogens.

Mammalian transcription factors (TFs) differ broadly in their nuclear mobility and sequencespecific/non-specific DNA binding affinity. How these properties affect the ability of TFs to occupy their specific binding sites in the genome and modify the epigenetic landscape is unclear. Here we combined live cell quantitative measurements of mitotic chromosome binding (MCB) of 502 TFs, measurements of TF mobility by fluorescence recovery after photobleaching, single molecule imaging of DNA binding in live cells, and genome-wide mapping of TF binding and chromatin accessibility. MCB scaled with interphase properties such as association with DNA-rich compartments, mobility, as well as large differences in genome-wide specific site occupancy that correlated with TF impact on chromatin accessibility. As MCB is largely mediated by electrostatic, non-specific TF-DNA interactions, our data suggests that non-specific DNA binding of TFs enhances their search for specific sites and thereby their impact on the accessible chromatin landscape.

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