CHARACTERIZATION OF A NOVEL N-TERMINAL PEPTIDE IN HUMAN ASPARTYL-TRANSFER-RNA SYNTHETASE - ROLES IN THE TRANSFER OF AMINOACYL-TRANSFER-RNA FROM AMINOACYL-TRANSFER-RNA SYNTHETASE TO THE ELONGATION-FACTOR 1-ALPHA

The kinetics of the N-terminal 32 residue deleted human aspartyl-tRNA synthetase (hDRS Delta 32) was analyzed, The kinetics of aspartyl-aden ylate formation and Asp-tRNA synthesis by hDRS Delta 32 were indisting uishable from those of hDRS, However, the dissociation of Asp-tRNA fro m hDRS Delta 32 was much faster than that of hDRS, Unlike hDRS Delta 3 2-catalyzed aspartylation of tRNA was not affected by the elongation f actor 1 alpha. Two N-terminal peptides of hDRS, hDRS(T5-E26) and hDRS( D12-R27), were synthesized, Both peptides bind to tRNA-Sepharose, Both peptides, hDRS(T5-E26) and hDRS(D12-R27), are monomeric and oligomeri ze at high peptide concentration or in 50% propylene glycol, The pepti de hDRS(T5-E26) showed little alpha-helical content as analyzed by CD spectroscopy, while hDRS(D12-R27) showed appreciable alpha-helical con tents in nonpolar solvents. These results suggest that the N terminus in hDRS may mediate the slow release of Asp-tRNA and facilitate the in teraction of the hDRS Asp-tRNA complex with the elongation factor 1 al pha. The demonstration of alpha-helix formation of the hDRS N-terminal peptide is consistent with the hypothetical amphiphilic helix of the N terminal extension in hDRS. A model for the transfer of Asp-tRNA fro m hDRS to elongation factor 1 alpha is presented,