Poxviruses: an emerging portrait of biological strategy.

The meeting offered ample evidence that the field of poxvirology has truly come of age. Many investigators were attracted to the field by its experimental feasibility; indeed, the virions are "in vitro transcription systems" and the genome is a "cDNA library." The viral life cycle is synchronous and rapid and can be studied genetically and biochemically in a wide range of cell types. What has become clear is that the virus also offers a unique opportunity to dissect a range of biological problems. The enzymes involved in nucleic acid metabolism are numerous and easily accessible to study; vaccinia is fast evolving into a model system of choice for structure-function studies. The cascade of gene expression offers a chance to investigate in detail the mechanism of trans-acting factors that determine transcriptional specificity, as well as a system to probe the role of genome "chromatin" in dictating the accessibility of transcriptional units. But perhaps the most lasting impression of vaccinia is as a virus that encodes a unique repertoire of proteins governing its survival within the host. Among these are proteins that may activate the next round of cells to be infected, reduce the activation of cells responsible for the inflammatory response, and sabotage the biochemical cascades of host defenses. Never before has a virus held up a mirror so intriguing and so informative.