Zinc deficiency and the Euglena gracilis chromatin: formation of an .alpha.-amanitin-resistant RNA polymerase II

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Abstract
Both the single DNA-dependent RNA polymerase found in Zn-deficient (-Zn) Euglena gracilis and the RNA polymerase III from Zn-sufficient (+Zn) cells were isolated by methods previously used to purify polymerases I and II. 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 analog, 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 Zn is the functional metal while Cu, Mn, Fe and Mg are absent. The -Zn enzyme is at least 4 orders of magnitude more resistant to .alpha.-amanitin (.alpha.-A) than the class II polymerase. 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.-A-sensitive polymerase II.