Transiently misacylated tRNA is a primer for editing of misactivated adenylates by class I aminoacyl-tRNA synthetases.
The genetic code depends on amino acid fine structure discrimination by aminoacyl-tRNA synthetases. For isoleucyl- ( IleRS) and valyl-tRNA synthetases (ValRS), reactions that hydrolyze misactivated noncognate amino acids help to achieve high accuracy in aminoacylation. Two editing pathways contribute to aminoacylation fidelity: pretransfer and post-transfer. In pretransfer editing, the misactivated amino acid is hydrolyzed as an aminoacyl adenylate, while in post-transfer editing a misacylated tRNA is deacylated. Both reactions are dependent on a tRNA cofactor and require translocation to a site located approximately 30 A from the site of amino acid activation. Using a series of 3'-end modified tRNAs that are deficient in either aminoacylation, deacylation, or both, total editing (the sum of pre- and post-transfer editing) was shown to require both aminoacylation and deacylation activities. These and additional results with IleRS are consistent with a post-transfer deacylation event initiating formation of an editing-active enzyme/tRNA complex. In this state, the primed complex processively edits misactivated valyl-adenylate via the pretransfer route. Thus, misacylated tRNA is an obligatory intermediate for editing by either pathway.[1]References
- Transiently misacylated tRNA is a primer for editing of misactivated adenylates by class I aminoacyl-tRNA synthetases. Nordin, B.E., Schimmel, P. Biochemistry (2003) [Pubmed]
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