Aminoacyl-tRNA modification

Aminoacyl-tRNA synthetases Degradation of proteins, peptides, and glycopeptides Nucleoproteins Protein modification... 

A ribozyme activity that led to RNA-modifications that are analogous to the 5 -5 pyrophosphate caps of eukaryotic RNA transcripts was selected by Huang and Yarns [84]. Actually the author s intention was to isolate ribozymes which catalyze the formation of a mixed anhydride between an amino acid carboxylate and a 5 -terminal phosphate of an RNA, an activity that is chemically analogous to the activation of amino acids by ATP catalyzed by aminoacyl tRNA synthetases. However, while the selected ribozymes did... 

Essential modification reactions of aminoacyl-tRNAs. In bacteria the initiator tRNA needed to start the synthesis of a polypeptide is initially aminoacyl-ated by methionine, but the metluonyl-tRN ArV1rl must then be N-formylated by transfer of a formyl group from N10-formyltetrahydrofolate (Fig. 15-18 ... 

Tsao ML, Tian F, Schultz P. Incorporation of unnatural reactive amino acids into phage display libraries using ortiiogonal mutant aminoacyl-tRNA synthetases for post-translational modification. PCT Int. Appl. 2007 114. 

Feng L, Sheppard K, Namgoong S, Amhrogelly A, Polycarpo C, Randan L, Tumhula-Hansen D, Soil D. Aminoacyl-tRNA synthesis by pre-translational amino acid modification. RNA Biol. 2004 1 16-20. 

Selenium is incorporated into Se-requiring enzymes by the modification of serine. This serine is not modified when it is in the free state or when it occurs in a polypeptide chain. The serine residue in question is modified when it occurs boimd to transfer RNA, that is, eis the aminoacyl-tRNA derivative. Seryl-tRNA is converted to selenocysteinyl-tRNAby the action of selenocysteine synthase (Stur-chler et al, 1993). The codon for selenocysteine is UGA (TGA in DNA UGA in mRNA). The fact that this particular triplet of bases codes for an amino acid is very imusual, as UGA normally is a stop codon. Stop codons occur in mRNA and signal the termination of synthesis of the protein however, in the case of the UGA codons that code for selenocysteine residues, regions of the mRNA that lie beyond the coding sequence somehow convert the UGA from a codon that halts translation to one that codes for selenocysteine (Figure 10.55). The structure of selenocysteine is shown in Figure 10.56. 

Modification of an elongation factor for translation (EF-Tu) to accept aminoacyl-tRNAs carrying nonnatural amino acids and to bring them into the A site of ribosome. 

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