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At least 541 records · Page 30Linked to original sources
PubMed2005

De novo genetic codes and pure translation display.

It is appealing to envision engineering translation for the genetically encoded synthesis of new classes of molecules. The complete reassignment of codons to unnatural amino acids at one or two non-adjacent sites per protein has already found wide utility (see other papers in this volume). This has been achieved by suppression at stop codons or rarely used sense codons in crude systems and in vivo. However, competing aminoacyl-tRNAs, aminoacyl-tRNA synthetases, and release factors limit efficiencies and generalization. We maximize flexibility by omitting the competing components and by reconstituting translation from His-tagged initiation and elongation factors. This approach opens up all 64 codons to amino acid reassignment and has allowed incorporation of several adjacent unnatural amino acids for the study of translation mechanism. One potential application is "peptidomimetic evolution" for ligand discovery. Toward this goal, we have demonstrated the display of polypeptides on their mRNAs in a purified translation system, termed "pure translation display."

Amino Acids↗
PubMed2006

A chemical toolkit for proteins--an expanded genetic code.

Recently, a method to encode unnatural amino acids with diverse physicochemical and biological properties genetically in bacteria, yeast and mammalian cells was developed. Over 30 unnatural amino acids have been co-translationally incorporated into proteins with high fidelity and efficiency using a unique codon and corresponding transfer-RNA:aminoacyl-tRNA-synthetase pair. This provides a powerful tool for exploring protein structure and function in vitro and in vivo, and for generating proteins with new or enhanced properties.

Amino Acids↗
PubMed1992

Evolution of mitochondrial genomes and the genetic code.

Mitochondrial genomes are clearly marked by a strong tendency towards reductive evolution. This tendency has been facilitated by the transfer of most of the essential genes for mitochondrial propogation and function to the nuclear genome. The most extreme examples of genomic simplification are seen in animal mitochondria, where there also are the greatest tendencies to codon reassignment. The reassignment of codons to amino acids different from those designated in the so called universal code is seen in part as an expression of the reduction of the number of genes used by these genomes to code for tRNA species. The driving force for the reductive evolution of mitochondrial genomes is identified with two population genetic effects which may also be operating on populations of parasites.

Animals↗
PubMed2006

An asymmetric underlying rule in the assignment of codons: possible clue to a quick early evolution of the genetic code via successive binary choices.

Aminoacyl-tRNA synthetases (aaRSs) are responsible for creating the pool of correctly charged aminoacyl-tRNAs that are necessary for the translation of genetic information (mRNA) by the ribosome. Each aaRS belongs to either one of only two classes with two different mechanisms of aminoacylation, making use of either the 2'OH (Class I) or the 3'OH (Class II) of the terminal A76 of the tRNA and approaching the tRNA either from the minor groove (2'OH) or the major groove (3'OH). Here, an asymmetric pattern typical of differentiation is uncovered in the partition of the codon repertoire, as defined by the mechanism of aminoacylation of each corresponding tRNA. This pattern can be reproduced in a unique cascade of successive binary decisions that progressively reduces codon ambiguity. The deduced order of differentiation is manifestly driven by the reduction of translation errors. A simple rule can be defined, decoding each codon sequence in its binary class, thereby providing both the code and the key to decode it. Assuming that the partition into two mechanisms of tRNA aminoacylation is a relic that dates back to the invention of the genetic code in the RNA World, a model for the assignment of amino acids in the codon table can be derived. The model implies that the stop codon was always there, as the codon whose tRNA cannot be charged with any amino acid, and makes the prediction of an ultimate differentiation step, which is found to correspond to the codon assignment of the 22nd amino acid pyrrolysine in archaebacteria.

Amino Acyl-tRNA Synthetases↗