DNA‐Dependent RNA Polymerase from the Archaebacterium Sulfolobus acidocaldarius

Purified DNA‐dependent RNA polymerase from Sulfolobus acidocaldarius is composed of 10 different subunits, one of which is present as four copies. Their molecular weights are 122000, 101000, 44000, 32000, 24000, 17500, 13800, 11800 (four copies), 11200, 10800, summing up to a total M r of 423500. The sedimentation velocity is 13.5 S, indicating that at 0.5 M NH 4 Cl the enzyme exists in the monomeric form. At pH 9.2 in cellogel electrophoresis two of the subunits migrate towards the cathode. The composition is quite different from that of a typical eubacterial RNA polymerase. Its complexity reminds one of eucaryotic RNA polymerase. Maximal transcription of DNA from a Halobacterium halobium phage φH (φH DNA) proceeds at pH 8.5 and 75 °C. The enzyme is stable up to 75 °C and strictly requires a DNA template. φH DNA and poly[d(A‐T) · d(A‐T)] are the most efficient. The temperature dependence of the transcription rate is characteristic for the template. Actinomycin D and heparin prevent transcription, while rifampicin, streptolydigin and α‐amanitin have no effect. During storage, even at −70°C, the enzyme loses its activity to transcribe φH DNA, whereas transcription of poly[d(A‐T) · d(A‐T)] remains unaffected.