[Selectivity of A-site on Escherichia coli ribosomes in relation to deacylation of transfer RNA].
To evaluate the equilibrium affinity of several deacylated tRNA from E. coli and yeast tRNA(Phe) for the A site of poly(U)- and poly(A)-programmed E. coli ribosomes, we studied their inhibitory effect on the subsequent binding of the template-cognate ternary complex EFTu*GTP* [14C]aminoacyl-tRNA. At 0 degree C and 10 mM Mg2+, affinities of template-cognate tRNAs were characterized by association constants Ka approximately 1-7.10(7) M-1. At least for the poly(U)-programmed system, this value practically coincided with the one determined earlier from direct nonenzymatic binding. Splitting off two 3'-terminal nucleotides did not appreciably change the tRNA affinity, that is, these nucleotides do not form direct contacts with the A site. Noncognate tRNAs were 120-1800-fold weaker as inhibitors; there was no considerable correlation between tRNA affinity for the A site and the extent of noncomplementarity of its anticodon to the template. The only except was tRNA(Tyr) in the system with poly(U), which displayed an affinity only 9-fold lower than that of template-cognate tRNA(Phe). The results obtained here show that the mRNA-programmed ribosomal A site reveals selectivity not only for energy-dependent enzymatic binding of aminoacyl-tRNA, but also for nonenzymatically bound nonacylated tRNA. Even in this simplified model, the selectivity is much higher than that observed when codons interact with anticodons in solution without ribosomes.
Ivanov
Iu V
IuV
Saminskiĭ
E M
EM
D000215:Acylation; D000926:Anticodon; D001665:Binding Sites; D004926:Escherichia coli / Q000378:metabolism*; D012343:RNA, Transfer / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D013698:Templates, Genetic
D000926:Anticodon; D012343:RNA, Transfer
Selektivnost' A-saĭta ribosom Escherichia coli po otnosheniiu k dezatsilirovannoĭ tRNK.