| Abstract: | Both the single DNA-dependent RNA polymerase found in zinc-deficient (-Zn) Euglena gracilis and the RNA polymerase III from zinc-sufficient (+Zn) cells have been isolated by methods previously used to purify polymerases I and II Falchuk, K. H., Mazus, B., Ulpino, L., & Vallee, B. L. (1976) Biochemistry 15, 4468; Falchuk, K. H., Mazus, B., Ulpino, L., & Vallee, B. L. (1977) Biochem. Biophys. Res. Commun. 74, 1206]. Like class II polymerases, the enzyme from -Zn organisms elutes from DNA-cellulose and phosphocellulose with 0.6 M NaCl and 0.35 M NH4Cl, respectively. It is inhibited by 8-hydroxyquinoline, 8-hydroxyquinoline-5-sulfonic acid, alpha,alpha'-bipyridyl, dipicolinic acid, and 1,10-phenanthroline (OP); 4,7-phenanthroline, the nonchelating analogue, does not inhibit. The pKI(OP) of this enzyme is identical with that of polymerase II but distinct from those of polymerases I and III. Elemental analysis confirms that zinc is the functional metal while copper, manganese, iron, and magnesium are absent. However, the -Zn enzyme is at least 4 orders of magnitude more resistant to alpha-amanitin (alpha-A) than the class II polymerase. Further, its response to alpha-A is unlike that of either polymerase I or polymerase III. Thus, -Zn cells contain a single, alpha-amanitin-resistant (alpha-Ar) RNA polymerase, whose behavior otherwise resembles that of the alpha-amanitin-sensitive polymerase II. |
