Post-transcriptional modification in archaeal tRNAs: identities and phylogenetic relations of nucleotides from mesophilic and hyperthermophilic Methanococcales

Post-transcriptional modifications in archaeal RNA are known to be phylogen etically distinct but relatively little is known of tRNA from the Methanoco cci, a lineage of methanogenic marine euryarchaea that grow over an unusual ly broad temperature range. Transfer RNAs from Methanococcus vannielii, Met hanococcus maripaludis, the thermophile, Methanococcus thermolithotrophicus , and hyperthermophiles Methanococcus jannaschii and Methanococcus igneus w ere studied to determine whether modification patterns reflect the close ph ylogenetic relationships inferred from small ribosomal subunit RNA sequence s, and to examine modification differences associated with temperature of g rowth. Twenty-four modified nucleosides were characterized, including the c omplex tricyclic nucleoside wyosine, characteristic of position 37 in tRNA( Phe) and known previously only in eukarya, plus two new wye family members of presently unknown structure. The hypermodified nucleoside 5-methylaminom ethyl-2-thiouridine, reported previously only in bacterial tRNA at the firs t position of the anticodon, was identified by liquid chromatography-electr ospray ionization mass spectrometry in four of the five organisms. The ribo se-methylated nucleosides, 2'-O-methyladenosine, N-2,2'-O-dimethylguanosine and N-2,N-2,2'-O-trimethylguanosine, were found only in hyperthermophile t RNA, consistent with their proposed roles in thermal stabilization of tRNA.