mRNA-displayed proteins after individual steps of selection round 6 analyzed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. (A) Gel for ‘60 min selection’. (B) Gel for ‘5 min selection’. TL: translation; OdT: eluate after purification by oligo-(dT) cellulose chromatography; Flag: eluate from Flag affinity purification; RT: reverse transcription of ³⁵S-Met-labeled protein-RNA fusions to verify efficiency of reverse transcription; RT-³²P: reverse transcription in presence of ³²P-α-dATP to include ³²P-labeling in the cDNA; Dialysis: sample recovered after dialysis into Flag buffer; Flag II: eluate from second Flag affinity purification. The ligation reaction was performed with biotinylated 3΄-OH-substrate in presence of complementary splint oligonucleotide.