期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1974
卷号：71
期号：5
页码：1790-1794
DOI：10.1073/pnas.71.5.1790
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Mouse myeloma cells have previously been shown (L. B. Schwartz, V. E. F. Sklar, J. A. Jaehning, R. Weinmann & R. G. Roeder, submitted for publication) to contain two chromatographically distinct forms of RNA polymerase III (designated IIIA and IIIB). The enzymes are unaffected by low [α]-amanitin concentrations which completely inhibit RNA polymerase II, but they exhibit characteristic inhibition curves (identical for IIIA and IIIB) at higher toxin concentrations. RNA polymerase I was unaffected at all [α]-amanitin concentrations tested. Myeloma RNA polymerases II, IIIA, and IIIB appear to be inhibited by the same mechanism, since the toxin rapidly blocks chain elongation by each enzyme. The characteristic [α]-amanitin sensitivity of RNA polymerase III has been employed in studies of the function(s) of the class III RNA polymerases. Isolated myeloma nuclei and nucleoli conti[n]ue to synthesize RNA via the endogenous RNA polymerases when incubated in vitro. With nuclei, newly synthesized 4S precursor (pre-4S) and 5S RNA species were detected by electrophoretic analysis either of the total nuclear RNA or of the RNA released into the supernatant during incubation. The synthesis of both pre-4S and 5S RNA species was inhibited by [α]-amanitin, but only at high concentrations; and the [α]-amanitin inhibition curves for these RNAs were identical to those obtained for solubilized RNA polymerases IIIA and IIIB. In control experiments it was shown that the endogenous RNA polymerase II activity of isolated nuclei was inhibited by [α]-amanitin concentrations similar to those required to inhibit purified enzyme II. However, 40-50% of the endogenous activity of nuclei and 100% of the endogenous activity of purified nucleoli was completely resistant to the high [α]-amanitin concentrations necessary to inhibit the RNA polymerase III activities. These experiments rule out nonspecific inhibitory effects in the endogenous systems. These results unequivocally demonstrate the role of RNA polymerase III (IIIA and/or IIIB) in the synthesis of (pre) 4S RNAs and a 5S RNA species.
