Display efficiency of GFP fused to the different sites of the gpD head protein in lambda. Lambda phage clones displaying GFP as N-terminal (GFP-N-λ), C-terminal (GFP-C-λ) fusions or fused to the new positions inside of the gpD protein (GFP-2-λ, GFP-3-λ, GFP-4-λ), were tested by ELISA using anti-GFP antibody. λKM4 wild type phage was tested as a negative control. On the abscissa are indicated the amount of wild type phage measured in pfu. The amounts of all other phages used in ELISA have been normalized relative to wild type phage, so as to have identical number of physical particles per well. ELISA was performed by using anti-gpV antibody-coated plates and the displayed GFP was revealed by using an anti-GFP AP-conjugated antibody. Results are expressed as A=A405-A620. Data reported are the average values of assays performed in duplicate. Error bars represent the standard deviation of the mean.