Partitioning of tRNA-dependent Editing between Pre- and Post-transfer Pathways in Class I Aminoacyl-tRNA Synthetases
作者:Morana Dulic、Nevena Cvetesic、John J. Perona、Ita Gruic-Sovulj
DOI:10.1074/jbc.m110.133553
日期:2010.7
Measurements of the microscopic rate constants for amino acid transfer to tRNA in IleRS and the related valyl-tRNAsynthetase (ValRS) further suggest that pre-transfer editing in IleRS is an enzyme-catalyzed activity residing in the synthetic active site. In this model, the balance between pre-transfer and post-transfer editingpathways is controlled by kinetic partitioning of the noncognate aminoacyl-adenylate
Recognition of Adenosine Residues by the Active Site of Poly(A)-specific Ribonuclease
作者:Niklas Henriksson、Per Nilsson、Mousheng Wu、Haiwei Song、Anders Virtanen
DOI:10.1074/jbc.m109.043893
日期:2010.1
Poly(A)-specific ribonuclease (PARN) is a mammalian 3'-exoribonuclease that degrades poly(A) with high specificity. To reveal mechanisms by which poly(A) is recognized by the active site of PARN, we have performed a kinetic analysis using a large repertoire of trinucleotide substrates. Our analysis demonstrated that PARN harbors specificity for adenosine recognition in its active site and that the nucleotides surrounding the scissile bond are critical for adenosine recognition. We propose that two binding pockets, which interact with the nucleotides surrounding the scissile bond, play a pivotal role in providing specificity for the recognition of adenosine residues by the active site of PARN. In addition, we show that PARN, besides poly(A), also quite efficiently degrades poly(U), similar to 10-fold less efficiently than poly(A). The poly(U)-degrading property of PARN could be of biological significance as oligo(U) tails recently have been proposed to play a role in RNA stabilization and destabilization.
Aminoacyl Transfer Rate Dictates Choice of Editing Pathway in Threonyl-tRNA Synthetase
作者:Anand Minajigi、Christopher S. Francklyn
DOI:10.1074/jbc.m110.105320
日期:2010.7
Aminoacyl-tRNA synthetases hydrolyze aminoacyl adenylates and aminoacyl-tRNAs formed from near-cognate amino acids, thereby increasing translational fidelity. The contributions of pre- and post-transfer editing pathways to the fidelity of Escherichia coli threonyl-tRNA synthetase (ThrRS) were investigated by rapid kinetics. In the pre- steady state, asymmetric activation of cognate threonine and noncognate serine was observed in the active sites of dimeric ThrRS, with similar rates of activation. In the absence of tRNA, seryl-adenylate was hydrolyzed 29-fold faster by the ThrRS catalytic domain than threonyl-adenylate. The rate of seryl transfer to cognate tRNA was only 2-fold slower than threonine. Experiments comparing the rate of ATP consumption to the rate of aminoacyl-tRNA(AA) formation demonstrated that pre- transfer hydrolysis contributes to proofreading only when the rate of transfer is slowed significantly. Thus, the relative contributions of pre- and post-transfer editing in ThrRS are subject to modulation by the rate of aminoacyl transfer.