This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Bacteriophage Epsilon15 is a generalized transducing phage infecting the human/animal pathogen Salmonella enterica serovar Anatum. Epsilon 15 has been studied for its ability to recognize and bind O-antigen as well as its capacity to alter host lipopolysaccharide in the lysogenic state. The viral protein responsible for O-antigen recognition is the tailspike protein. The virion contains at least six structural proteins and an approximately 40 kb dsDNA genome of known sequence. At the sequence level, the structural proteins most closely resemble the Bcep phages of Burkholderia, a human pathogen affecting cystic fibrosis patients. The virion structural proteins and chromosome together make a particle with a mass of approximately 66 Megadaltons and a diameter of roughly 650[unreadable]. Jon King's lab has used mass spectrometric methods to identify those open reading frames encoding virion structural proteins. The structure of this virus will reveal the arrangement of structural proteins and, in particular, the configuration of those subunits more directly involved in attachment to the host and passage of DNA into the cytoplasm. A genetic approach is now underway to isolate amber mutants in virus structural proteins. Macromolecular subassemblies formed during infections with these mutant phage will be purified and imaged by reconstruction. These mutant phage will also serve as reagents for imaging the interactions between virus and lipopolysaccharide and receptor proteins at the surface of the host.