DNA-dependent RNA polymerases for Schneider 2-L cells of Drosophila. I. Preliminary characterization.

The DNA-dependent RNA polymerases of Schneider 2-L cells of Drosophila melanogaster are described. These cells contain five readily detectable forms of this enzyme, polymerases Ia, Ib, IIIa, II, and IIIb, which elute from DEAE-Sephadex at 0.08, 0.12, 0.15, 0.20, and 0.22 M ammonium sulfate, respectively. RNA polymerases IIIa and IIIb, which each constitute about 5-10% of the total RNA polymerase activity in Drosophila embryos, are found to constitute 30 and 10%, respectively, of the total polymerase activity in cultured cells. The two form III polymerases are further characterized by in vitro response to divalent cations and ionic strength, template utilization, and sensitivity to alpha-amanitin. Verification of the class III designation of these two polymerases is provided by their sensitivity to only very high levels of alpha-amanitin (50% inhibition at approximately 800 micrograms/ml), their 10-fold greater activity on poly[d(A-T)], and their elution from DEAE-cellulose at lower ionic strengths that from DEAE-Sephadex.