Valenzuela P, Hager G L, Weinberg F, Rutter W J
Proc Natl Acad Sci U S A. 1976 Apr;73(4):1024-8. doi: 10.1073/pnas.73.4.1024.
Homogeneous RNA polymerase III (RNA nucleotidyltransferase III) has been obtained from yeast. The subunit composition of the enzyme was examined by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The enzyme is composed of 12 putative subunits with molecular weights 160,000, 128,000, 82,000, 41,000, 40,500, 37,000, 34,000, 28,000, 24,000, 20,000, 14,500, and 11,000. The high-molecular-weight subunits and several of the smaller subunits of yeast RNA polymerase III are clearly different from those of enzymes I and II, indicating a distinct molecular structure. However, the molecular weights of some of the small subunits (41,000, 28,000, 24,000, and 14,500) appear to be identical to those of polymerases I and II. Thus, it is possible that the three classes of enzymes in yeast have some common subunits. As in other eukaryotes, yeast polymerase II is inhibited by relatively low concentrations of alpha-amanitin; however, contrary to what has been found in higher eukaryotes, yeast polymerase III is resistant (up to 2 mg/ml) to alpha-amanitin, while yeast polymerase I is sensitive to high concentrations of the drug (50% inhibition at 0.3 mg/ml). These results establish the existence of RNA polymerase III in yeast and provide a structural basis for the discrimination of the three functional polymerases in eukaryotes.
已从酵母中获得了均一的RNA聚合酶III（RNA核苷酸转移酶III）。在十二烷基硫酸钠存在的情况下，通过聚丙烯酰胺凝胶电泳对该酶的亚基组成进行了检测。该酶由12个推定的亚基组成，分子量分别为160,000、128,000、82,000、41,000、40,500、37,000、34,000、28,000、24,000、20,000、14,500和11,000。酵母RNA聚合酶III的高分子量亚基和几个较小的亚基与酶I和酶II的亚基明显不同，表明其具有独特的分子结构。然而，一些小亚基（41,000、28,000、24,000和14,500）的分子量似乎与聚合酶I和聚合酶II的相同。因此，酵母中的这三类酶有可能具有一些共同的亚基。与其他真核生物一样，酵母聚合酶II受到相对低浓度的α-鹅膏蕈碱的抑制；然而，与在高等真核生物中发现的情况相反，酵母聚合酶III对α-鹅膏蕈碱具有抗性（高达2mg/ml），而酵母聚合酶I对高浓度的该药物敏感（在0.3mg/ml时50%抑制）。这些结果证实了酵母中存在RNA聚合酶III，并为区分真核生物中的三种功能性聚合酶提供了结构基础。
