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SPOTLIGHT

Articles of Significant Interest Selected from This Issue by the Editors

Rotaviruses are large RNA viruses that assemble through a complex morphogenesis process in which the last steps occur in the endoplasmic reticulum (ER). Maruri-Avidal et al. (p. 5368-5380) have begun to dissect the role of ER chaperones in the morphogenesis of the virus by silencing the expression of components of the two well-characterized ER folding systems. The results suggest that grp78, calnexin, PDI, and calreticulin are involved in quality control of rotavirus morphogenesis by promoting the timely trimming of carbohydrate chains of VP7 and NSP4, the correct formation of VP7 disulfide bonds, and the incorporation of properly folded VP7 into infectious virus. The complexity of the steps of rotavirus assembly in the ER provide a useful model to study the organization of the network of chaperones involved in maintaining quality control in this organelle.

Insight into Host Cell Reprogramming for Simian Virus 40 DNA Replication

Simian virus 40 (SV40) DNA replication in infected primate cells occurs under conditions in which host DNA damage-signaling pathways are activated. Zhao et al. (p. 5316-5328) have begun to dissect how this process unfolds. They show that SV40 T antigen and Mre11-Rad50-Nbs1 assemble in viral replication centers and that T-antigen binding to a host ubiquitin ligase leads to proteasome-dependent destruction of Mre11-Rad50-Nbs1. Remarkably, both processes depend on ATM kinase activity. These results suggest that SV40 DNA replication resembles host DNA repair or replication fork recovery pathways.

Visualization of Herpes Simplex Virus 1 Assembly in the trans-Golgi Network

It has been suggested that herpes simplex virus 1 (HSV-1) acquires its final envelope at cytoplasmic membranes, but the precise cellular sites for definitive envelopment of HSV-1 are not defined. Sugimoto et al. (p. 5198-5211) examined HSV-1 assembly sites by using imaging techniques with triply fluorescent HSV-1 and provide evidence for the assembly of all three types of herpesvirus proteins—capsid, tegument, and envelope—in the trans-Golgi network (TGN). These findings suggest that the TGN is the site of HSV-1 final envelopment.

New Insights into RNA Interference in Plants

Plant viruses produce RNA silencing-associated, small interfering RNAs (siRNAs) of viral origin upon infection. Donaire et al. (p. 5167-5177) show that Tobacco rattle virus (TRV)-derived siRNAs of sense and antisense polarities are generated from all regions of the viral genome through nucleolytic processing by Dicer-like activities (DCL2, DCL3, and DCL4). The distribution of TRV siRNAs is heterogeneous and reveals a differential contribution throughout the TRV genome to siRNA formation. The biogenesis of TRV siRNAs and antiviral defense is heavily dependent on the combined activity of RNA-dependent, RNA polymerases RDR1, RDR2, and RDR6.

Influenza Virus Transmission under Tropical Conditions

Influenza epidemics recur with marked seasonality in temperate climates during the cold winter months but occur more sporadically in tropical and subtropical climates. Lowen et al. (p. 5650-5652) present data gathered using a guinea pig model suggesting that this difference in epidemiology is due to differences in the predominant mode of influenza virus spread in different climates. While aerosol transmission was blocked under warm conditions (30°C), contact transmission remained efficient at 30°C and all humidities studied. These findings provide new insights into the mechanisms underlying a familiar phenomenon: the seasonality of influenza in humans.

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