Phleboviruses encapsidate their genomes by sequestering RNA bases

Rift Valley fever and Toscana viruses are human pathogens for which no effective therapeutics exist. These and other phleboviruses have segmented negative-sense RNA genomes that are sequestered by a nucleocapsid protein (N) to form ribonucleoprotein (RNP) complexes of irregular, asymmetric structure, previously uncharacterized at high resolution. N binds nonspecifically to single-stranded RNA with nanomolar affinity. Crystal structures of Rift Valley fever virus N-RNA complexes reconstituted with defined RNAs of different length capture tetrameric, pentameric and hexameric N-RNA multimers. All N-N subunit contacts are mediated by a highly flexible α-helical arm. Arm movement gives rise to the three multimers in the crystal structures and also explains the asymmetric architecture of the RNP. Despite the flexible association of subunits, the crystal structures reveal an invariant, monomeric RNP building block, consisting of the core of one N subunit, the arm of a neighboring N, and four RNA nucleotides with the flanking phosphates. Up to three additional RNA nucleotides bind between subunits. The monomeric building block is matched in size to the repeating unit in viral RNP, as visualized by electron microscopy. N sequesters four RNA bases in a narrow hydrophobic binding slot and has polar contacts only with the sugar-phosphate backbone, which faces the solvent. All RNA bases, whether in the binding slot or in the subunit interface, face the protein in a manner that is incompatible with base pairing or with “reading” by the viral polymerase.     

Structural basis for the constitutive activity and immunomodulatory properties of the Epstein-Barr virus-encoded G protein-coupled receptor BILF1

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Evaluation of the impact of Exomite Pro™ on Varroa mite (Varroa destructor) populations and honeybee (Apis mellifera) colonies: efficacy,side effects and residues

In this research, we examined the application of thymol-based powder, directly over the top of the brood frames in colonies with different population in a 2-year study. The efficacy against mites, the side effects on bees and the contamination of honey were studied comparably to thymol-based gel treatment. In one-store colonies, thymol-based powder treatment gave average efficacy 64.5 % and did not differ significantly from thymol-based gel treatment (65.4 %). The natural mortality in control colonies was 41.4 % and the corrected efficacy (E _T) during 2 years was 39.4 and 40.9 %, respectively. In two-store bee colonies, the application of thymol-based powder on top of each hive body gave higher E _T (45,4 %) than on top of the double body hive (40.4 %), without statistically significant differences. The average concentration of thymol residues in honey 24 days after the application was 368 and 1,119 μg kg^?1 for the honey of colonies treated with thymol-based powder and thymol-base gel, respectively.