The site of hydrolysis by rabbit reticulocyte peptidyl-tRNA hydrolase is the 3'-AMP terminus of susceptible tRNA substrates

Abstract

The preceding paper (Gross, M., Starn, T.K., Rundquist, C., Crow, P., White, J., Olin, A., and Wagner, T. (1992) J. Biol. Chem. 267, 2073-2079) reported the purification and partial characterization of rabbit reticulocyte peptidyl-tRNA hydrolase. In this article we demonstrate that, unlike bacterial and yeast peptidyl-tRNA hydrolase which act by deacylation, the reticulocyte enzyme hydrolyzes N-acylaminoacyl-tRNA to N-acylaminoacyl-AMP. Reticulocyte lysate has a separate enzyme, that we have isolated and termed aminoacyl-AMP deacylase, which hydrolyzes N-acylaminoacyl-AMP and aminoacyl-AMP, recycling the amino acid and nucleotide components. The action of this enzyme is relatively specific for the N-acylaminoacyl-AMP generated by peptidyl-tRNA hydrolase, since it is much less active with N-acylaminoacyl-adenosine and inactive with N-acylaminoacyl-ACCAC, N-acylaminoacyl-tRNA, or aminoacyl-tRNA. The tRNA product of peptidyl-tRNA hydrolase action is tRNA missing only its 3'-AMP terminus (tRNA(c-c)), since reaminoacylation requires tRNA nucleotidyltransferase but not CTP. The 3' exonucleolytic action of reticulocyte peptidyl-tRNA hydrolase is specific to susceptible tRNA substrates, since it does not hydrolyze CACCA, CACCA-N-acylamino acid, polyuridylic acid, or the 3' polyadenylate tail of globin mRNA, and, since its ability to hydrolyze Escherichia coli f[3H]Met-tRNA(fMet) is not reduced by excess 5 S or 28 S ribosomal RNA and is reduced only slightly by excess tRNA(c-c). Reticulocyte peptidyl-tRNA hydrolase also hydrolyzes th 3'-AMP terminus of deacylated tRNA. This property may explain why the 3'-terminal AMP of tRNA undergoes turnover in reticulocytes and reticulocyte lysate, since we find that such turnover in gel-filtered reticulocyte lysate is increased under conditions where aminoacylation is reduced.