TY - JOUR T1 - A virus DNA gate: Zipping and unzipping the packed viral genome JF - Proceedings of the National Academy of Sciences JO - Proc Natl Acad Sci USA SP - 8403 LP - 8404 DO - 10.1073/pnas.0903670106 VL - 106 IS - 21 AU - Rao, Venigalla B. Y1 - 2009/05/26 UR - http://www.pnas.org/content/106/21/8403.abstract N2 - Tailed bacterial viruses (bacteriophages) are ubiquitously distributed in nature and are likely the most abundant organisms on the biosphere (1). Spending most of their time outside of the host, a bacterial cell, in often hostile external environments, they come to “life” upon encountering the receptor molecules on the host cell surface. The virus consists of a head (capsid) into which the DNA (genome) is packaged and a tail that delivers the genome into the bacterium. The capsid is pressurized because of packing of highly negatively-charged, relatively rigid dsDNA to near-crystalline density (≈500 μg/mL). The internal capsid pressure, ≈6 MPa or &gt;10 times that of bottled champagne (2), provides a driving force for delivery of viral genome into host cell. One of the longstanding questions in phage biology has been how these viruses contain the DNA pressure and trigger release only upon recognition of a specific host cell. In this issue of PNAS, a study by Lhuillier et al. (3) describes the pseudoatomic structure of a DNA gate from the Bacillus subtilis bacteriophage SPP1, which “zips” the capsid after the genome is packaged and unzips it when the virus is ready to infect the host. It is a compelling story, which began with the first in vitro virus assembly experiments described by Edgar and Wood &gt;40 years ago (4) and is applicable not only to phages but also to large eukaryotic viruses such as herpes viruses.In the assembly of a typical tailed bactreiophage, a capsid shell of precise dimensions is assembled, often with a single protein subunit, around a protein scaffold. A mushroom-shaped dodecameric portal ring (Fig. 1) acts as an initiator of head assembly and remains at the special 5-fold vertex of the otherwise isometric capsid, facilitating all subsequent transactions: DNA packaging, tail attachment, and DNA delivery. The scaffold … 1E-mail: rao{at}cua.edu ER -