RNA modification tRNA modification PMID:12697167 The covalent alteration of one or more nucleotides within a tRNA molecule to produce a tRNA molecule with a sequence that differs from that coded genetically [source: GO]. Transfer RNA (tRNA) is structurally unique among nucleic acids in harboring an astonishing diversity of post-transcriptionally modified nucleoside. Over 80 modified nucleosides have been characterized. The nature of nucleoside modification varies from simple methylation to extensive 'hypermodification' of the canonical bases. Two of the most radically modified nucleosides known to occur in tRNA are queuosine and archaeosine, both of which are characterized by a 7-deazaguanosine core structure. pathway UPa:UPA00481 GO:0006400 transfer RNA modification