|Home | About | Journals | Submit | Contact Us | Français|
Noroviruses are the major cause of nonbacterial gastroenteritis in humans. Taube et al. (p. 5695-5705) and Katpally et al. (p. 5836-5841), respectively, describe atomic structures of the murine norovirus 1 (MNV-1) receptor-binding protruding (P) domain and high-resolution cryo-electron microscopy image reconstructions of MNV-1 and the related calicivirus, rabbit hemorrhagic disease virus (RHDV). Atomic structures of the MNV-1 P domain show that surface-exposed loops adopt at least two different conformations and encompass a neutralizing epitope. The image reconstructions demonstrate flexibility of the MNV-1 and RHDV P domains relative to the virion shell. Together, these studies show a genus-independent flexibility in the P domain of the calicivirus capsid which likely plays an important role in facilitating virus-host interactions.
Filoviruses and most retroviruses contain a conserved chain reversal region within their glycoprotein fusion subunits. A model for the function of this region in fusion was proposed for human T-cell leukemia virus type 1. Delos et al (p. 5687-5694) now extend this model to the alpharetrovirus, avian sarcoma/leucosis virus (ASLV), and the filovirus, ebolavirus Zaire. Dissection of ASLV fusion into its main functional steps reveals a Phe 439 residue that operates early and a His 428 residue that affects the pH of later fusion steps. These results highlight additional similarities between retroviral and filoviral fusion subunits and demonstrate the importance of the chain reversal region for multiple steps in enveloped virus fusion.
Host cells contain many large noncoding RNAs, often found antisense to known open reading frames. However, the functions of these RNAs are largely unknown. Xu and Ganem (p. 5465-5475) examined viral RNAs that are antisense to the RTA protein of Kaposi's sarcoma-associated herpesvirus. These “noncoding” RNAs do not regulate RTA, but rather, they appear to be mRNAs encoding multiple short peptides. These findings raise the possibility that the mammalian proteome contains a universe of previously unsuspected peptides.
How herpesviruses are transported in an anterograde fashion from the neuronal cell body to the distant synapse is not well understood. Maresch et al. (p. 5528-5539) show by high-resolution electron microscopy that enveloped virions of the porcine pseudorabies virus are present within vesicles intraaxonally and in terminal growth cones. Remarkably, these virions leave the neuron by exocytosis. Results of this study suggest that complete virions rather than subviral components are the relevant cargo for herpesvirus neuroinvasion by the anterograde route.
Viruses have evolved a variety of mechanisms to antagonize innate host defenses. Rose et al. (p. 5656-5669) show that infection with the murine coronavirus mouse hepatitis virus (MHV) inhibits interferon (IFN)-dependent and Sendai virus-induced expression of IFN-stimulated genes (ISGs). Curiously, the IFN-signaling pathway involving STAT1/STAT2 phosphorylation and nuclear translocation appears to be intact. The capacity of MHV to delay Sendai virus-mediated ISG production involves limitation of IRF-3 function as a transcription factor. This work underscores the multiple, cell type-specific strategies used by coronaviruses to inhibit type I IFN responses.