Polyphenylalanine, formation

Several other tj s are available, which employ electrostatic or hydrophobic interactions or metal chelate formation including polyarginine (79), polyphenylalanine or polycysteine (80), and dipeptide His-Trp (81). 

Sparsomycin, a sulfur-containing antibiotic, inhibits protein synthesis in mammalian and bacterial cells. Tryptophan administration before or after sparsomycin did not affect the hepatic polyribosomal disaggregation or the decreased protein synthesis due to sparsomycin.188 A possible explanation for the lack of effect by tryptophan may be due to sparsomycin s ability to cause fall-off ribosomes, which are defective as indicated by the decreased formation of polyphenylalanine when assayed in vitro with poly(U).207... 

Reactions initiated by H and OH would lead to these and other radicals. H could react at the backbone C-H and at the carbonyl group, forming the peptide radical, but is more likely to add to aromatic or heterocyclic amino acid moieties, forming side chain radicals. OH could also react by abstraction or, more likely, by addition. The formation of addition radicals facilitates crosslinking through the side chains. Studies with polyphenylalanine peptides confirm such crosslinking and show how crosslinked products with and without hydroxyl groups can be produced [15, 16]. 

These were the foundations on which our work was to be built. Joe Speyer and I were at the preparatory stage of the project (we had received all labeled amino acids ordered for the experiments and were determining the size of our polynucleotides) when the rumor of Nirenberg and Matthaei s momentous discovery reached us in August 1961. While studying the effect of RNAs from different sources on protein synthesis in a cell-free system from E. coli, they discovered that the homopolyribonucleotide poly(U) promoted the formation of the homopolypeptide polyphenylalanine. Thereby, the genetic code was broken. 

These were isolated in our laboratory by Skoultchi, Ono, Waterson and Beaud. I will designate the factors here in the now accepted way as EF-Ts, EF-G and EF-Tu at the time they were called S, Sj and S3, respectively. All three were needed for the poly(U)-promoted formation of polyphenylalanine from the Phe-tRNA. The studies on peptide-chain elongation in vitro were greatly facilitated by this model system in which chain elongation takes place without proper chain initiation and termination, and in the absence of initiation and termination factors and initiator tRNA. 

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