<p>The archaeosine tRNA-guanine transglycosylase (tgt) differs from the tgt of <taxon tax_id="562">Escherichia coli</taxon> and other bacteria in the site of action and the modification that results. It exchanges 7-cyano-7-deazaguanine (preQ0) with guanine at position 15 of archaeal tRNA; this nucleotide is subsequently converted to archaeosine, found exclusively in the archaea. In contrast, bacterial tgt catalyzes the exchange of preQ0 or preQ1 for the guanine base at position 34; this nucleotide is subsequently modified to queuosine (<db_xref db="INTERPRO" dbkey="IPR004803"/>). <taxon tax_id="2234">Archaeoglobus fulgidus</taxon> has both enzymes.</p> Archaeosine tRNA-ribosyltransferase