(Figure 6A and B). This suggests that these enzymes include either a domain devoted to measuring the length of the D-loop of tRNA or an active site able to sense the difference of a bulged D-loop. More surprising is the fact that quite unexpectedly, archaea and bacteria use kingdom-speciﬁc identity elements for efﬁcient and speciﬁc transamidation of Asp-tRNAAsn by their GatCAB AdTs (Figure 6). The archaeal AdTs recognize the V-region of tRNA, which con- stitutes a sort of hinge between the acceptor arm, i.e. the primitive tRNA and the anticodon arm which was added later in evolution to form the modern L-shaped tRNA mole- cule (30). In bacteria the ﬁrst base pair of the acceptor arm could serve as strong transamidation identity determinant because this base pair is conserved in all tRNAAsn species and it is not present in any tRNAAsp molecule (Figure 6A and B). This contrasts with archaea where the ﬁrst base pair is conserved in tRNAAsn and tRNAAsp. Therefore, dis- crimination between tRNAAsn and tRNAAsp had to be based on another part of tRNA (Figure 6C and D). Finally, based on our bioinformatics strategy that was validated by the iden- tiﬁcation of bacterial and archaeal transamidation identity elements, we predict that the same structural elements medi- ate speciﬁc tRNA-dependent formation of Gln in bacteria. Therefore, bacteria very likely use a unique set of transami- dation identity elements for AdT-catalyzed biosynthesis of both amide amino acids. ACKNOWLEDGEMENTS The authors thank Dr D. Drainas for support and discussion, Drs A. Theobald-Dietrich and J. Rudinger for M.barkeri extracts, Dr Marielle Bauzan (IBSM, IFR88, Marseille) for M.barkeri cells and Drs Z. Mamuris and P. Markoulatos for materials. This work was supported by the Universite´ Louis Pasteur de Strasbourg, the Centre National de la Recherche Scientifique and by the Hellenic General Secretariat of Research and by the Technology and the University of Thessaly Research Committee. Grants supporting this work were from the Association pour la Recherche sur le Cancer (ARC), from ACI Microbiologie fondamentale et applique´e, maladies infectieuses, environnement et bioterrorisme, from ACI Biologie cellulaire, mole´culaire et structurale and from EGIDE (Platon). M.B. and M.B. are doctoral fellows of the Ministe`re de l’Education Nationale de la Recherche et de la Technologie (MENRT) and the Association pour la Recherche sur le Cancer, respectively. Funding to pay the Open Access publication charges for this article was provided by Centre National de la Recherche Scientifique. Conflict of interest statement. None declared. REFERENCES 1. Ibba,M., Becker,H.D., Stathopoulos,C., Tumbula,D.L. and So¨ll,D. 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