() Schematic illustration of the formation of streptavidin–tRNA fusion using puromycin–tRNA, which contains a puromycin moiety in the place of 3′ terminal aminoacyl-adenosine and a four-base anticodon CCCG

Abstract

<p><b>Copyright information:</b></p><p>Taken from " selection of tRNAs for efficient four-base decoding to incorporate non-natural amino acids into proteins in an cell-free translation system"</p><p>Nucleic Acids Research 2006;34(5):e44-e44.</p><p>Published online 20 Mar 2006</p><p>PMCID:PMC1405820.</p><p>© The Author 2006. Published by Oxford University Press. All rights reserved</p> The puromycin–tRNA binds to ribosomal A site and accepts a streptavidin polypeptide chain as an analog of aminoacyl-tRNA in response to a four-base CGGG codon at 3′ terminus of streptavidin mRNA in a cell-free translation. The resulting streptavidin–puromycin–tRNA may be translocated to the P-site. In this case, the next aminoacyl-tRNA binds to the vacant ribosomal A site, but can not accept the polypeptide chain because of the amide bond of puromycin–tRNA. The resulting streptavidin–tRNA fusion is released from the ribosome complex by the addition of EDTA. () Schematic illustration of the selection system of tRNAs. Step 1, a DNA pool encoding tRNAs containing a four-base anticodon CCCG is transcribed by T7 RNA polymerase to tRNA(-CA) pool. Step 2, the tRNA(-CA) pool is ligated with pdCp-Puromycin by T4 RNA ligase to generate puromycin–tRNA. Step 3, a streptavidin mRNA containing a four-base CGGG codon at C-terminus is translated in an cell-free translation system in the presence of the puromycin–tRNA. Puromycin–tRNAs that successfully decode the CGGG codon form ribosome–mRNA–streptavidin–tRNA complex. Step 4, the streptavidin–tRNA fusion is dissociated from the complex by the addition of EDTA. Step 5, the streptavidin–tRNA fusion is recovered with biotin-coated magnetic beads. Step 6, the streptavidin–tRNA fusion is dissociated from the beads, and then the tRNA moiety is subjected to RT–PCR. Step 7, the tRNA genes are regenerated by overlap-extension PCR with a T7 promoter primer, which are used as template DNAs in the next round of selection