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SPOTLIGHT

Articles of Significant Interest Selected from This Issue by the Editors

APOBEC3G is a cytidine deaminase that inhibits cellular genome invasion by retroviruses and retrotransposons. Using tandem affinity purification and mass spectrometry, Gallois-Montbrun et al (p. 2165-2178) identified multiple cellular RNA-binding proteins as components of APOBEC3G-containing ribonucleoprotein complexes. Confocal microscopy further revealed that APOBEC3G localizes to cytosolic microdomains (P bodies and stress granules) that are rich in RNA processing factors. These findings suggest that APOBEC3G may be regulated through its interplay with cellular RNA processing factors and sites of RNA metabolism and thus may modulate cellular RNA function.

Retinoblastoma Family Mediates the Transcriptional Response during Senescence Driven by Human Papillomavirus Repression

HeLa cervical carcinoma cells rapidly undergo senescence when the human papillomavirus type 18 E7 gene in these cells is repressed by the bovine papillomavirus (BPV) E2 protein. Johung et al. (p. 2102-2116) used microarrays to demonstrate that the transcriptional response to the BPV E2 protein in senescing HeLa cells is entirely dependent on E7 repression and activation of the retinoblastoma (Rb) family. These results indicate that a transcriptional cascade driven by the Rb tumor suppressor pathway plays a primary role in senescence induced by viral oncogene repression. Comparison to senescent fibroblasts suggests that this Rb-driven cascade also plays an important role in replicative senescence.

The Old World and New World Alphaviruses Use Different Mechanisms for Inhibition of Cellular Transcription

The New World alphaviruses evolved separately from those of the Old World. Nevertheless, both groups have developed a common characteristic: their replication interferes with cellular transcription and eventually with the development of a cellular response to viral replication. Garmashova et al. (p. 2472-2484) provide intriguing new evidence that the transcriptional shutoff caused by the New World alphaviruses depends on the capsid protein, while the Old World alphaviruses employ the nonstructural protein nsP2 to achieve the same goal. These data provide fresh insights into alphavirus evolution, particularly regarding the formation of the recombinant alphaviruses, and the development of alphavirus vaccines.

Recovery of Reoviridae Family Member Bluetongue Virus from Single-Stranded RNA

Bluetongue virus uncoats during entry to produce a transcriptionally active core particle that extrudes plus-sense transcripts of the segmented double-stranded RNA genome into the host cell cytoplasm. Boyce and Roy (p. 2179-2186) show that infectious bluetongue virus is recovered from cells that have been transfected only with viral transcripts. This discovery suggests a novel approach to achieving helper virus-independent reverse genetics for the Reoviridae family as well as an experimental system for investigating the fate of early RNA and the initial stages of the replication cycle.

P58^IPK: Can It Put the Virulence in Pandemic Influenza?

Many viruses encode proteins that help evade cellular antiviral defense mechanisms. Goodman et al. (p. 2221-2230) show that influenza virus also takes advantage of a cellular protein for the same purpose. Studies using genetically deficient mouse embryonic fibroblasts reveal that influenza virus requires P58^IPK for efficient viral mRNA translation and that P58^IPK inhibition of PKR is needed for this effect. Parallel studies using vesicular stomatitis virus and reovirus suggest that recruitment of P58^IPK may be a common strategy used by RNA viruses to evade the antiviral effects associated with PKR activation.

Human Immunodeficiency Virus Type 1 Targeting of Dendritic Dells in a Model of Parenteral Transmission

Selection for human immunodeficiency virus type 1 (HIV-1) strains that use the coreceptor CCR5 occurs during parenteral transmission, but the cells responsible for this selection have not been defined. Cameron et al. (p. 2297-2306) provide evidence that dendritic cells (DCs) are the cells infected at highest frequency by these isolates. However, enhanced and selective infection is seen only for immature DCs transiently exposed to HIV-1. Viral RNA is expressed at low levels unless the infected immature DCs interact with T cells, providing a pathway favoring the early expansion of CCR5-binding HIV-1 into T cells.

Insights into the Recent Spread of West Nile Virus

West Nile virus (WNV) is an emerging virus that was first reported in North America in the New York City area in the summer of 1993, where it resulted in a serious outbreak of encephalitis in human, avian, and equine populations. Using new population genetics techniques, Snappin et al. (p. 2531-2534) show that the two genotypes of WNV, NY99 and WN02, exhibit different rates of epidemiological population growth and that the growth rate of the currently circulating WN02 strain has recently declined. These results suggest that WNV has reached its peak prevalence in North America.

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