Binding of FBPAs to GFPs and spectrally shifted GFP variants. (A) Comparison of G16 and AP3 binding to FPs show that AP3 binds GFP and EGFP with higher affinity than G16, and that binding to the coral protein Azami-green is of much lower affinity. (B) Filter-binding assay shows similar affinity of AP3 to GFP-related proteins. (C) Hill plot fits of data shown in (A) and (B) show similar affinity of AP3 to GFP-related proteins.