title: Genetic analysis of structural proteins in the adsorption apparatus of bacteriophage epsilon 15.
abstract: OBJECTIVE
  To probe the organizational structure of the adsorption apparatus of bacteriophage epsilon 15 (E15) using genetic and biochemical methodology
  
  
  METHODS
  Hydroxylamine was used to create nonsense mutants of bacteriophage E15. The mutants were then screened for defects in their adsorption apparatus proteins, initially by measuring the concentrations of free tail spike proteins in lysates of cells that had been infected by the phage mutants under non-permissive growth conditions. Phage strains whose infected cell lysates contained above-average levels of free tail spike protein under non-permissive growth conditions were assumed to contain nonsense mutations in genes coding for adsorption apparatus proteins. These mutants were characterized by classical genetic mapping methods as well as automated sequencing of several of their genes. Finally, sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography were used to examine the protein compositions of the radioactive particles produced when the various mutants were grown on a non-permissive host cell in the presence of (35)S-methionine and co-purified along with E15wt phage on CsCl block gradients.
  
  
  RESULTS
  Our results are consistent with gp4 forming the portal ring structure of E15. In addition, they show that proteins gp15 and gp17 likely comprise the central tube portion of the E15 adsorption apparatus, with gp17 being more distally positioned than gp15 and dependent upon both gp15 and gp16 for its attachment. Finally, our data indicates that tail spike proteins comprised of gp20 can assemble onto nascent virions that contain gp7, gp10, gp4 and packaged DNA, but which lack both gp15 and gp17, thereby forming particles that are of sufficient stability to survive CsCl buoyant density centrifugation.
  
  
  CONCLUSIONS
  The portal ring (gp4) of E15 is bound to tail spikes (gp20) and the tail tube (gp15 and gp17); gp17's attachment requires both gp15 and gp16.
authors.affiliation: Jared A Guichard, Paula C Middleton, Michael R McConnell, Department of Biology, Point Loma Nazarene University, San Diego, CA 92106, United States.
authors.forename: Jared A
authors.initials: JA
authors.lastname: Guichard
authors.forename: Paula C
authors.initials: PC
authors.lastname: Middleton
authors.forename: Michael R
authors.initials: MR
authors.lastname: McConnell
keywords: Epsilon15; Salmonella phages; Virion structure