The stability of rat liver ribonucleic acid in vivo after methylation with methyl methanesulphonate or dimethylnitrosamine

Abstract

1. RNA was isolated from rat liver at selected times after the intraperitoneal injection of either [(14)C]methyl methanesulphonate (50mg/kg) or [(14)C]dimethylnitrosamine (2mg/kg). These doses were chosen to minimize effects due to toxicity. 2. Two methods of extraction and purification of RNA were used and an analysis of the radioactivity present was made by column chromatography of acid hydrolysates of the purified RNA. 3. The extent of methylation of guanine, the principal site of alkylation in rat liver RNA, was determined at times up to 14 days after injection. Although dimethylnitrosamine is a potent liver carcinogen and methyl methanesulphonate is not carcinogenic to rat liver, the rate of disappearance of 7-methylguanine from RNA was similar for both compounds, with a half-life of about 3.5 days. 4. An estimate of the biological half-life of rRNA was made by using [(3)H]orotic acid. A half-life of 5 days was obtained and this was not affected by injecting animals with unlabelled methyl methanesulphonate at the same dosage of 50mg/kg used in the studies of RNA methylation. 5. After administration of labelled orotic acid, reutilization of labelled RNA degradation products probably results in an overestimation of the biological half-life for rRNA. It is suggested that non-toxic doses of methylating agents such as methyl methanesulphonate and dimethylnitrosamine may prove to be a more effective way of accurately estimating the biological turnover of RNA species.

Comparative Studies of the Hepatocarcinogen N,N-Dimethylnitrosamine in vivo: Reaction Sites in Rat Liver DNA and the Significance of their Relative Stabilities

“…RNA studies described previously have demonstrated radioactive labelling of the -j purine bases via the 1-carbon pool (Craddock and Magee, 1963;Whittle, 1969;McElhone et al, 1971). In the present work metabolic labelling of DNA (expressed as dpm/,umol of purine bases) was 5-6 times less ( Fig.…”

“…In the present work metabolic labelling of DNA (expressed as dpm/,umol of purine bases) was 5-6 times less ( Fig. 7a and b) than in the corresponding rRNA study (McElhone et al, 1971). In DNA, thymine, and not cytosine, was also labelled by this process (Fig.…”

“…repair), the possibility exists that those few cells in division would be preferentially labelled and may not be representative of the whole tissue. Further infor- reported earlier (McElhone et al, 1971), substantially more radioactivity was incorporated into the purine bases after MMS treatment and this was attributed to the twenty-fold molar excess over the dosage of DMN which, allowing for the specific activity of the compounds, corresponded to about 7 times more radioactivity being administered in the MMS series. There was considerable animal variation in the extent of metabolic labelling of DNA but there was no evidence of a significant loss of label over the 21-day period ( Fig.…”

“…In the present report, a comparison is made of the methylation of liver DNA in rats treated with either the hepatic carcinogen N,N-dimethylnitrosamine (DMN) or methyl methanesulphonate (MMS) which is not known to be carcinogenic in rat liver. Using the low dosages detailed in the text, we have already presented evidence that the turnover of rRNA in rat liver cells in vivo is not altered for at least 14 days (McElhone, O'Connor and Craig, 1971; M. J. Capps, 1972).…”

Human Argonaute 2 Is Tethered to Ribosomal RNA through MicroRNA Interactions

“…The interaction of AGO2 with the rRNA is drastically reduced when cells are treated briefly with actinomycin D, which impairs Pol I transcription (34,35). This drug treatment would not affect the overall ribosomal levels, as their half-lives have been estimated to be up to 5 days (36). Thus, we conclude that interactions between AGO2 and the rRNA occurs at least in part within the nucleus.…”