n(2)-n(2)-dimethylguanosine and 7-methylguanine

7-Methylguanine (m7Gua), N2,N2-dimethylguanosine (m2(2)Guo), and pseudouridine (psi) are degradation products from RNA turnover and can be used as markers for the whole-body turnover of mRNA-cap, tRNA, and rRNA (in healthy individuals, urinary excretion of these catabolites follows a regular pattern; the relative molar ratio of psi:m7Gua:m2(2)Guo is approximately 100:19:6). HPLC methods were developed to measure serum concentrations of these RNA catabolites after deproteinization of the samples by ultrafiltration through microcollodion bags with a nominal exclusion Mr of 12,400. For healthy adults the following values (mean +/- SD) were found: psi, 2760 +/- 460 nmol/liter (n = 10); m7Gua, 129.7 +/- 24.0 nmol/liter (n = 13); m2(2)Guo, 31.0 +/- 3.7 nmol/liter (n = 9). The relative molar ratio of these substances in serum derived from our data is approximately 100:4.7:1.1. 7-Methylguanosine (m7Guo) added to serum is to a large extent converted to the corresponding free base, m7Gua, the form which is excreted in urine.

Topics: Adult; Chromatography, High Pressure Liquid; Guanine; Guanosine; Humans; Pseudouridine; Reference Values; RNA; Spectrophotometry, Ultraviolet; Ultrafiltration; Uridine

Modified building blocks are found in rRNA, tRNA and mRNA. Apart from pseudouridine these are mostly base- or ribose-methylated nucleosides. If these compounds are neither recycled nor degraded, they should be quantitatively excreted. For pseudouridine (Weissman et al., 1962; Dugaiczyk & Eiler, 1966) and 7-methylguanine (Craddock, Mattocks & Magee, 1968), urinary excretion has been shown to be quantitative. Since the turnover rates of rRNA and tRNA, which contain most of the modified nucleosides, are similar within a given tissue, compounds found only in these two classes of RNA should appear in urine in approximately the proportions in which they are present in the body. Using pseudouridine as internal standard, we show this indeed to be likely for one of the major RNA catabolites in human urine, N2,N2-dimethylguanosine, a compound present only in tRNA. By contrast, 7-methylguanine is excreted in threefold larger amounts than can be explained by joint provenance from tRNA and rRNA only; the remainder we assume to come from the 'cap' structure of mRNA, known for its high turnover. We suggest that one can use the urinary excretion of pseudouridine, N2,N2-dimethylguan(os)ine and 7-methylguanine to assess the whole-body turnover rates in man of rRNA, tRNA and mRNA, respectively. Such data may be useful to define whole-body metabolic activity.

Topics: Animals; Guanine; Guanosine; Half-Life; Humans; Nucleosides; Pseudouridine; Rats; RNA; RNA, Messenger; RNA, Ribosomal; RNA, Transfer; Tissue Distribution

Urinary excretion of the non-reusable modified RNA catabolites pseudouridine (psi), 7-methylguanine (m7Gua) and N2,N2-dimethylguanosine (m2(2)Guo) was measured in preterm infants and in adults. The values (in mumol/mmol of creatinine) were: for preterm and 'small for gestational age' infants (n = 26; number of samples = 38) psi = 164 (SD 32), m7Gua = 39.1 (SD 9.0), m2(2)Guo = 10.6 (SD 2.1); for adults (n = 32) psi = 25.3 (SD 3.1), m7Gua = 4.8 (SD 0.89), m2(2)Guo = 1.53 (SD 0.42). Our measurements were compared with an expectation derived from the average cellular distribution of psi, m7Gua and m2(2)Guo between rRNA, tRNA and mRNA. m2(2)Guo occurs exclusively in tRNA, psi in both rRNA and tRNA, and m7Gua in all three RNA classes, in proportions which can be estimated for the steady state. Urinary excretion of psi and m2(2)Guo should reflect their steady-state distribution, since rRNA and tRNA have been shown to have similar turnover rates in mammalian tissues. We conclude that we can use the excretion of m2(2)Guo to assess whole-body tRNA turnover. Since tRNA contains psi in a constant proportion to m2(2)Guo, the proportion of urinary psi stemming from tRNA can be estimated, and the remainder (approximately 60-65%) is an indicator of rRNA turnover. Finally, the excretion of m7Gua far exceeds the proportion predicted to come from rRNA and tRNA. We ascribe this excess (approximately 60-70% of the total) to the turnover of the mRNA 'cap'-structure, which is typical for all higher organisms. mRNA turnover is known to be much higher than that or rRNA or tRNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adolescent; Adult; Female; Guanine; Guanosine; Half-Life; Humans; Infant, Newborn; Infant, Premature; Infant, Small for Gestational Age; Male; Middle Aged; Pseudouridine; RNA; RNA, Ribosomal; RNA, Transfer