2--o-methylguanosine and 3-methyluridine

We have systematically investigated the duplex to hairpin conversion of oligoribonucleotides under the aspect of nucleobase methylation. The first part of our study refers to the self-complementary sequence rCGCGAAUUCGCGA, which forms a stable Watson-Crick base paired duplex under various buffer conditions. It is shown that this sequence is forced to adopt a hairpin conformation if one of the central 6 nt is replaced by the corresponding methylated nucleotide, such as 1-methylguanosine N(2),N(2)-dimethylguanosine, N(6),N(6)-dimethyladenosine (m(6)(2)A) or 3-methyluridine. On the other hand, the duplex structure is retained and even stabilized by replacement of a central nucleotide with N(2)-methylguanosine (m(2)G) or N(4)-methylcytidine. A borderline case is represented by N(6)-methyladenosine (m(6)A). Although generally a duplex-preserving modification, our data indicate that m(6)A in specific strand positions and at low strand concentrations is able to effectuate duplex-hairpin conversion. Our studies also include the ssu ribosomal helix 45 sequence motif, rGACCm(2)GGm(6)(2)Am(6)(2)AGGUC. In analogy, it is demonstrated that the tandem m(6)(2)A nucleobases of this oligoribonucleotide prevent duplex formation with complementary strands. Therefore, it can be concluded that nucleobase methylations at the Watson-Crick base pairing site provide the potential not only to modulate but to substantially affect RNA structure by formation of different secondary structure motifs.

Topics: Adenosine; Base Pairing; Cytidine; Guanosine; Hydrogen Bonding; Inosine; Methylation; Nucleic Acid Conformation; Oligoribonucleotides; RNA; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Thermodynamics; Uridine

The urinary excretion of six methylated ribonucleosides was measured in a case of anorexia nervosa during the first eight weeks of therapy. Four phases can be distinguished. Highly elevated values are found in a clearly catabolic situation. Immediately after onset of therapy when catabolism is stopped but nutrition still inadequate the excretion of RNA-catabolites is lowered markedly. As soon as normocaloric nutrition is reached after two weeks, a short but clearcut peak-excretion can be observed. Finally, the excretion of methylated RNA-catabolites is stabilized on an intermediate level after three to six weeks, when nutrition is constantly normocaloric and weight continues to increase linearly.

Topics: Adenosine; Adolescent; Anorexia Nervosa; Female; Guanosine; Humans; Inosine; Nucleosides; Uridine