Buhler J M, Iborra F, Sentenac A, Fromageot P
J Biol Chem. 1976 Mar 25;251(6):1712-7.
The subunits of yeast RNA polymerases A(I) and B(II) were characterized using several techniques. The present studies demonstrate that the A and B enzymes possess three subunits, which are indistinguishable on the basis of molecular weight, isoelectric point, and fingerprint pattern. The three common subunits belong to the small molecular weight components of the enzymes. By polyacrylamide gel electrophoresis with sodium dodecyl sulfate they migrate with apparent molecular weights of 27,000, 23,000, and 14,500, respectively. A two-dimensional subunit mapping technique on polyacrylamide gel was used to separate the subunits according to isoelectric point and molecular weight. The common polypeptides co-migrated on three spots corresponding to isoelectric points of 9.2 (27,000), 4.5 (23,000), and 4.6 (14,500). The fingerprints of the 35S-labeled tryptic peptides of the presumptive common subunits were found to be essentially identical. Finally, the presence of common subunits was supported by the fact that antibodies against pure RNA polymerase A cross-react with and inhibit RNA polymerase B. Except for the common subunits, it is likely that RNA polymerases A and B are primarily made of distinct gene products for the following reasons. A total of 13 polypeptide chains are present in enzyme A, whereas 10 polypeptides are found in enzyme B. The molecular weight, isoelectric point, and sulfur content of the majority of these polypeptide chains are different in the two enzymes. No similarity was found in the 35S-peptide fingerprint from a number of A and B subunits of slightly different molecular weight. Finally, antibodies against the largest subunit from RNA polymerase A do not cross-react with or inhibit RNA polymerase B. The data are discussed in terms of structural organization of eukaryotic RNA polymerases.
运用多种技术对酵母RNA聚合酶A（I）和B（II）的亚基进行了表征。目前的研究表明，A酶和B酶拥有三个亚基，基于分子量、等电点和指纹图谱，它们无法区分。这三个共同的亚基属于酶的小分子量组分。通过十二烷基硫酸钠聚丙烯酰胺凝胶电泳，它们的表观分子量分别为27,000、23,000和14,500。采用聚丙烯酰胺凝胶二维亚基图谱技术，根据等电点和分子量分离亚基。这些共同的多肽在对应于等电点9.2（27,000）、4.5（23,000）和4.6（14,500）的三个位点上共同迁移。推定的共同亚基的35S标记胰蛋白酶肽的指纹图谱基本相同。最后，针对纯RNA聚合酶A的抗体与RNA聚合酶B发生交叉反应并抑制它，这一事实支持了共同亚基的存在。除了共同亚基外，RNA聚合酶A和B可能主要由不同的基因产物组成，原因如下。酶A中共有13条多肽链，而酶B中有10条多肽。这两种酶中大多数这些多肽链的分子量、等电点和硫含量都不同。在一些分子量略有不同的A和B亚基的35S肽指纹图谱中未发现相似性。最后，针对RNA聚合酶A最大亚基的抗体与RNA聚合酶B不发生交叉反应，也不抑制它。从真核RNA聚合酶的结构组织方面对这些数据进行了讨论。
