The Properties of a tRNA-Specific Adenosine Deaminase from Drosophila melanogaster Support an Evolutionary Link between Pre-mRNA Editing and tRNA Modification

Abstract

Pre-mRNA editing involving the conversion of adenosine to inosine is mediated by adenosine deaminases that act on RNA (ADAR1 and ADAR2). ADARs contain multiple double-stranded RNA(dsRNA)-binding domains in addition to an adenosine deaminase domain. An adenosine deaminase acting on tRNAs, scTad1p (also known as scADAT1), cloned from Saccharomyces cerevisiae has a deaminase domain related to the ADARs but lacks dsRNA-binding domains. We have identified a gene homologous to scADAT1 in the region of Drosophila melanogaster Adh chromosome II. Recombinant Drosophila ADAT1 (dADAT1) has been expressed in the yeast Pichia pastorisand purified. The enzyme has no activity on dsRNA substrates but is a tRNA deaminase with specificity for adenosine 37 of insect alanine tRNA. dADAT1 shows greater similarity to vertebrate ADARs than to yeast Tad1p, supporting the hypothesis of a common evolutionary origin for ADARs and ADATs. dAdat1 transcripts are maternally supplied in the egg. Zygotic expression is widespread initially and later concentrates in the central nervous system.

ACKNOWLEDGMENTS

We are grateful to Hyouta Himeno, Hirosaki University, for yeast tRNA-Ser; to H. Grosjean for tRNA substrates; to M. Affolter and A. Jarman for cDNA libraries; and to R. Reenan for sharing unpublished results.

This work was supported by the Medical Research Council, the University of Basel, the Swiss National Science Foundation, and the Louis-Jeantet Foundation for Medicine. A.P.G. was the recipient of a predoctoral fellowship from the Boehringer Ingelheim Fonds, and R.L. was supported by a grant from the European Union (via the Bundesamt für Bildung und Wissenschaft, Bern, Switzerland).