Function of the extra 5 '-phosphate carried by histidine tRNA

Among elongator tRNAs, tRNA specific for histidine has the peculiarity to p ossess one extra nucleotide at position -1. This nucleotide is believed to be responsible fur recognition by histidyl-tRNA synthetase. Here, we show t hat, in fact, it is the phosphate 5' to the extra nucleotide which mainly s upports the efficiency of the tRNA aminoacylation reaction catalyzed by Esc herichia coli histidyl-tRNA synthetase. In the case of the reaction of E. c oli peptidyl-tRNA hydrolase, this atypical phosphate is dispensable. Instea d, peptidyl-tRNA hydrolase recognizes the phosphate of the phosphodiester b ond between residues -1 and + I of tRNA(His). Recognition of the +1 phospha te of tRNA(His) by peptidyl-tRNA hydrolase resembles, therefore, that of th e 5'-terminal phosphate of other elongator tRNAs.