[en] The [³H]XTPs are used widely to monitor RNA synthesis in vitro. Recently, the authors discovered that they reflected only 40-45% of the true rate of nuclear RNA synthesis. Thus, when [8-¹⁴C]GTP was used, 1466 pmol [8-¹⁴C]GMP was incorporated per mg DNA/10 min. On the other hand, when [8-³H]GTP was used, only 564 pmol [8-³H]GMP was incorporated per mg DNA/10 min. There are three obvious factors that could have contributed to this greater than 2-fold difference in the apparent incorporation rate, none of which, the authors are able to conclude, are contributing factors. The data also show that the ³H label was removed after it was incorporated into RNA. Similar differences were observed when ³H and ¹⁴C labeled pairs of ATP, UTP and CTP were compared. Furthermore, when nuclei were fractionated into nucleolar and nucleoplasmic fractions and carried out RNA synthesis, the loss of ³H label was observed mainly from the nucleoplasmic fraction. (Auth.)

[en] For many years histones have been considered to be the gene suppressors in eukaryotic cells. Recently, the authors have found strong evidence indicating that poly-ADP-ribosylated histones, rather than histones, are the potent inhibitors of DNA-dependent RNA synthesis. They now report additional evidence for this concept: 1) using histone inhibitor isolated directly from nuclei, the authors are able to confirm their earlier findings that the inhibitor substances are sensitive to pronase, snake venom phosphodiesterase digestion and 0.1N KOH hydrolysis, and are resistant to DNase I and RNase A digestion, 2) the O.D. 260/O.D.280 ratio of the histone inhibitor is between pure protein and nuclei acid, suggesting the inhibitor substance is a nucleoprotein hybrid. This result directly supports the fact that the isolated histone inhibitor is radioactive poly (ADP-ribose) labeled, 3) commercial histones show big differences in inhibitor activity. The authors believe this reflects the variation in poly-ADP-ribosylation among commercial histones, and 4) 0.1N KOH hydrolysis eliminates the poly (ADP-ribose) radioactivity from the acceptor proteins as well as histone inhibitor activity. Yet, on gel, the inhibitor shows identical histone bands and stain intensity before and after hydrolysis, indicating the histones per se are qualitatively and quantitatively unaffected by alkaline treatment. This result strongly suggests that histones themselves are not capable of inhibiting DNA-dependent RNA synthesis