DNA-dependent RNA polymerase of thermoacidophilic archaebacteria

The component compositions of the DNA-dependent RNA polymerases of the extremely thermophilic, anaerobic sulfur-respiring archaebacteria Thermoproteus tenax and Desulfurococcus mucosus strongly resemble each other but also that of the RNA polymerase of Sulfolobus acidocaldarius suggesting that both organisms belong to the same novel order Thermoproteales, which together with the order represented by Sulfolobus, forms the thermoacidophilic branch of archaebacteria. The component pattern of the RNA polymerase of Thermoplasma acidophilum, which does not belong to this branch, also appears homologous. The archaebacterial type of the DNA-dependent RNA polymerase is thus characterized by 9-10 components yielding a characteristic pattern which resembles that of yeast RNA polymerase A(I). In contrast to the alpha subunit of eubacterial RNA polymerases, the third largest component of archaebacterial RNA polymerases, although similar in size, is present only one per enzyme monomer. The polymerases of T. tenax and D. mucosus, like those previously isolated from other archaebacteria, are completely resistant against 100 microgram/ml rifampicin and streptolydigin. The RNA polymerases of both organisms are highly thermostable. The enzyme from D. mucosus transcribes selectively and almost completely the H strand of phase T7 DNA.