Binding of conjugated gold to M13 phage with modified gp9. M13am9 phage propagated in E. coli K38 cells bearing a plasmid encoding gp9-DT7 or gp9-DHA, respectively, was tested for the presentation of the tag at the tip of the phage particles. The phage was incubated with the respective antibody and to protein A coupled immunogold particles (20 nm). M13am9-gp9-DT7 phage (A, B) and M13am9-gp9-DHA phage (C - E) were applied onto carbon coated grids, stained with 5% phosphotungstic acid and analysed by electron microscopy. For a control, M13 phage was applied (F). The scale bars correspond to 500 nm.