cDNA - protein fusions: covalent protein - gene conjugates for the in vitro selection of peptides and proteins.

We report a method for the synthesis of covalent cDNA-protein fusions for protein display applications. A branched mRNA template was developed which carries a peptidyl acceptor and a reverse transcription primer at the 3'-end. Translation in vitro followed by reverse transcription produced a protein covalently bonded to its encoding cDNA. Both single- and double-stranded cDNA-protein fusions were prepared. cDNA-protein fusions are stable in alkali and resistant to ribonucleases. Their simple preparation and their resistance towards degradation should make cDNA-protein fusions a useful tool for the in vitro selection and evolution of high affinity ligands from large libraries of polypeptides.