Nucleoside modification patterns in archaeal tRNAs determined by experimental MS/MS sequencing. The different modifications observed are reported on a typical cloverleaf two-dimensional structure. Underlined nucleotides are modified nucleotides with a mass corresponding to several possible chemistries for modifications, most of them corresponding to simple monomethylation products (see legend to Table 1). A “/” between two notations means a mixture of modifications. An “x” before a nucleotide, for example, xG, or after a modification symbol, for example, mx, means that the modification has not been formally identified (see text). Modified nucleotides indicated in brackets followed by an asterisk correspond to modifications deduced from the convergence of information from both the analysis of total tRNA and the presence of the gene coding for the corresponding modification enzyme in the genome of the particular archaeon. The modifications, uncertain or not completely identified, are underlined. Pseudouridines are not represented, except in the case of N1-methylpseudouridine (m1Y) because of the methyl group.
