Journal of Virology, August 2006, p. 7285-7286, Vol. 80, No. 15
0022-538X/06/$08.00+0 doi:10.1128/JVI.01161-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
| SPOTLIGHT |
Articles of Significant Interest Selected from This Issue by the Editors
Déjà Vu: Characterization of a Thermophilic Archaeal VirusIcosahedral double-stranded DNA (dsDNA) viruses are common in all three domains of life. However, genomic sequence analysis often fails to detect protein homology. The detailed characterization of the thermophilic Sulfolobus turreted icosahedral virus (STIV), which has an archaeal host, reveals that the composition of the virus particle is very similar to that of dsDNA viruses with eukaryotic and prokaryotic hosts. Using a mass spectrometry-based approach, Maaty et al. (p. 7625-7635) analyzed the proteins and lipids of STIV particles. Results from this work strengthen the hypothesis that viruses arose before the division of the major domains of life.
Ancient Origin and Pathogenic Potential of the Novel Human T-Cell Lymphotropic Virus Type 3
Human T-lymphotropic virus type 3 (HTLV-3) is a new virus recently identified in primate hunters in Central Africa. Switzer et al. (p. 7427-7438) used molecular dating to show that the ancestor of HTLV-3 is as old as HTLV-1 and HTLV-2, with an inferred divergence time of between 36 and 54 thousand years ago. Complete genome analysis identified molecular features in HTLV-3 that are more similar to HTLV-1 than to HTLV- 2, suggesting a pathogenic potential in HTLV-3-infected persons like that observed in HTLV-1 infection. These findings suggest that HTLV-3 may be prevalent and pathogenic and support the need for continued surveillance for this virus.
Uridylyation Reactions Catalyzed by Poliovirus Polymerase
Poliovirus RNA synthesis utilizes a protein primer, termed VPg, to which the viral polymerase can covalently add uridyl residues in solution. Richards et al. (p. 7405-7415) show that uridylyation substrates of the poliovirus RNA-dependent RNA polymerase also include larger precursors of VPg and, surprisingly, the polymerase itself. Depending on the RNA template, polymerase modification was either intramolecular or intermolecular, suggesting extensive conformational changes in the enzyme complexes. Phosphate stereochemistry experiments excluded the hypothesis that uridylyated polymerase was an intermediate in the formation of uridylyated VPg primer. The function of this posttranslational polymerase self-modification, also observed in infected cells, is not yet known.
Polyomavirus Middle T and Small T Proteins Control Early and Late Viral Gene Expression as Well as DNA Replication
The contributions of middle T (MT) and small T (ST) to the lytic cycle of polyomavirus are poorly understood. To dissect their roles, Chen et al. (p. 7295-7307) used a number of approaches, including coinfection of an MT/ST-null mutant with MT-expressing retroviruses. Their findings reveal contributions by ST and by each known and one new MT-regulated signaling pathway. Downstream ST and MT effects are mediated at the level of transcriptional activation, likely involving AP-1 and PEA3, and thus are not directly linked to MT/ST effects on the cell cycle. The pleiotropic roles of MT and ST result from the proximity of diverging early and late promoters flanking the enhancer and origin of DNA replication.
Influenza Virus Targets Differ in Mouse vs. Human Lung Cells
Influenza viruses infect lung epithelial cells. However, cell selectivity in mice compared to humans is not well described. Ibricevic et al. (p. 7469-7480) demonstrate that sialic acid receptors identified for avian and human influenza strains are highly cell-type specific and differ between mouse and human airway and alveolar epithelial cell populations. Knowledge of virus-strain and host-target differences have important implications for the evaluation of emerging avian and human virus infections in primary cell culture and animal models.
Insight into Chemokine Sequestration by Poxvirus Decoy Receptors
The EVM1 protein encoded by Ectromelia virus is a member of a highly conserved family of poxvirus chemokine-binding proteins. These secreted proteins interfere with host immune surveillance by competitively inhibiting CC-chemokine activation of host G protein-coupled receptors. To better understand the details underlying chemokine network sabotage, Arnold and Fremont (p. 7439-7449) have biophysically characterized the interaction between EVM1 and CCL2, CCL3, and CCL5. They present the crystal structure of EVM1 and a mutational analysis revealing key residues that comprise the binding interface. This study provides insight into the mechanism of chemokine inhibition employed by the poxvirus family of chemokine decoy receptors.
Journal of Virology, August 2006, p. 7285-7286, Vol. 80, No. 15
0022-538X/06/$08.00+0 doi:10.1128/JVI.01161-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
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