title: Wheat embryo ribonucleates. V. Generation of N2--dimethylguanylate when 'fully sequenced' homogeneous species of transfer RNA are used as substrates for wheat embryo methyltransferases.
abstract: When S-adenosly[methyl-14-C]methionine and various species of transfer RNA are used as substrates for wheat embryo methyltransferases, the principal site of guanylate-N-2 methylation can be shown to be a G-residue between the stems of the dihydrouridine and anticodon loops. This common site of guanylate-N-2 methylation is referred to as the interstem target site. 2. When the interstem target site is the non-terminal G-residue in a G-C-G-C sequence, as in the cases of Escherichia coli tRNA1-Leu, tRNA-Ile, and tRNA3-Ser, there is preponderant dimethylation to yield N-2-dimethylguanylate. 3. When the interstem target site is part of a U-C-G-U sequence, as in the case of E. coli tRNAf-Met, there is diminished dimethylation and correspondingly increased monomethylation to yield N-2-monomethylguanylate. 4. When the interstem target site is the non-terminal G-residue in an A-U-G-G sequence, as in the case of yeast tRNA-Asp, there is negligible dimethylation and almost exclusive monomethylation to yield N-2-monomethylguanylate. 5. The concerted way in which the primary, secondary, and tertiary structures of tRNA molecules might influence the efficacy of these methylations is the subject of a brief discussion. Attention is also focused on the evolutionary and molecular basis for the generally non-random distributions of methylated oligonucleotide sequences in ribosomal and transfer ribonucleates.
mesh_terms: D001483:Base Sequence; D002250:Carbon Radioisotopes; D002848:Chromatography, DEAE-Cellulose; D004926:Escherichia coli / Q000378:metabolism; D006150:Guanine Nucleotides / Q000096:biosynthesis*; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000494:pharmacology; D008956:Models, Chemical; D009690:Nucleic Acid Conformation; D012343:RNA, Transfer / Q000378:metabolism*; D012260:Ribonucleases / Q000494:pharmacology; D012436:S-Adenosylmethionine / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D012639:Seeds; D013329:Structure-Activity Relationship; D014908:Triticum / Q000201:enzymology; D012359:tRNA Methyltransferases / Q000378:metabolism*
chemical_list: D002250:Carbon Radioisotopes; D006150:Guanine Nucleotides; D012436:S-Adenosylmethionine; D012343:RNA, Transfer; D012359:tRNA Methyltransferases; D012260:Ribonucleases; D008274:Magnesium