Abstract
Adenosine or CpCpA trinucleoside diphosphate can be aminoacylated by phenylalanyl-tRNA synthetase [L-phenylalanine:tRNAPhe ligase (AMP forming), EC 6.1.1.20] when the reaction takes place in the presence of tRNAPhe deprived of its 3'' adenosine or pCpCpA terminus. Upon interaction with tRNA, a structural alteration of the enzyme''s active site is achieved. This process may be a determining step in the specificity of the aminoacylation reaction.