Abstract
Editing reactions are an essential part of biological information transfer processes that require high accuracy, such as replication, transcription, and translation. The editing in amino acid selection for protein synthesis by an aminoacyl-tRNA synthetase, the first proofreading process discovered in the flow of genetic information, prevents attachment of incorrect amino acids to tRNA. Of numerous editing reactions studied in vitro, only one, editing of homocysteine by methionyl-tRNA synthetase, has also been demonstrated in vivo. It is therefore unclear to what extent editing of errors is physiologically relevant. Here we show that isoleucyl- and leucyl-tRNA synthetases also edit homocysteine by cyclizing it to homocysteine thiolactone in the bacterium Escherichia coli. These and other data also suggest that metabolite compartmentation or channeling governs which synthetase participates in editing in bacterial cells.
Highlights
From the Department of Microbiology and Molecular Genetics, University of Medicine and DentistryNew Jersey Medical School, Newark, New Jersey 07103
The editing in amino acid selection for protein synthesis by an aminoacyl-tRNA synthetase, the first proofreading process discovered in the flow of genetic information, prevents attachment of incorrect amino acids to tRNA
In many cases differences in intrinsic binding energies of amino acids to aminoacyl-tRNA synthetases (AARS)1 are inadequate to give the required accuracy of translation. This has necessitated the evolution of a second determinant of specificity, proofreading or editing mechanisms that involve the expenditure of energy to remove errors in amino acid selection
Summary
In many cases differences in intrinsic binding energies of amino acids to aminoacyl-tRNA synthetases (AARS) are inadequate to give the required accuracy of translation. This has necessitated the evolution of a second determinant of specificity, proofreading or editing mechanisms that involve the expenditure of energy to remove errors in amino acid selection Ration of Hey into tRNA and protein in Escherichia coli [9], yeast [10], and some mammalian cells [11] It is unclear whether other editing reactions that have been demonstrated in vitro are physiologically relevant. To test whether exogenous Hey (taken up from the medium) can be edited by other aminoacyl-tRNA synthetases, cultures of E. coli cells that overproduce individual aminoacyl-tRNA synthetases have been incubated with Hey and assayed for Hey thiolactone by UV spectrometry and thin layer chromatography (TLC)
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