Summary. DNAs from 16 species of archaebacteria including 6 novel isolates were hybridized with 16S rRNAs from 7 species representing different orders or groups of the urkingdom of archaebacteria.The yields, normalized for the number of genes per ¡ig of DNA, and the temperature stabilities of all hybrids were determined and related to each other.A taxonomic tree constructed from such fractional stability data reveals the same major divisions as that derived from comparative cataloging of 16S rRNA sequences. The extreme halophiles appear however as a distinct order besides the three known divisions of methanogens.The methanogens, the halophiles and Thermoplasma form one of two clearly recognizable branches of the archaebacterial urkingdom. The order represented by Sulfolobus and the related novel order Thermoproteales form the other branch.Three novel genera, Thermoproteus, Desulfurococcus and the "stiff filaments" represent three families of this order.The extremely thermophilic methanogen Methanothermusfervidus belongs to the Methanobacteriales. SN1, a methanogen from Italy, appears as another species of the genus Methanococcus. Another novel methanogen, M3, represents a genus or family of the order Methanomicrobidles.
The component compositions of the DNA-dependent RNA polymerases of the extremely thermophilic. anaerobic sulfur-respiring archaebacteria Tliertnoproteus tenax and Desu/furococcus tnucosus strongly resemble each other but also that of the RNA polymerase of Siiljolobus acidocaldarius suggesting that both organisms belong to the same novel order Thermoproteales, which together with the order represented by Sulfolobiis, forms the thermoacidophilic branch of archaebacteria.The component pattern of the RNA polymerase of T/iermoplasmu acidophilum, which does not belong to this branch, also appears homologuous. 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(1). In contrast to the a subunit of eubacterial RNA polymerases, the third largest component of archaebacterial RNA polymerases, although similar in size, is present only once per enzyme monomer.The polymerases of T. feriax and D. niucosu.7, like those previously isolated from other archaebacteria, are completely resistant against 100 pg/ml rifampicin and streptolydigin.The RNA polymerases of both organisms are highly thermostable. The enzyme from D. inucosus transcribes selectively and almost completely the H strand of phage T7 DNA.The recently recognized highly thermophilic anaerobic sulfur-respiring Thermoproteales [I -31 and the order represented by Sulfolobus [4] form a distinct thermoacidophilic branch of the urkingdom of the archaebacteria [5,6] apart from that embracing the methanogens and the extreme lialophiles. This conclusion is based on comparative cataloging of 16-S rRNA oligonucleotide sequences according to Fox et al. [7] (Stackebrandt, Woese and Zillig, unpublished), on 16-S rRNA DNA cross-hybridization, as described by DeLey and DeSmedt [8,8a] and on the comparison of the component patterns of highly purified DNA-dependent RNA polymerases [2,3].This communication describes the isolation, the composition and some enzymic properties of the DNA-dependent RNA polymerases from representatives of two families of the novel order Thermoproteales, the Tliermoproteaceae [I] and the Desulfurococcaceae [2]. The results contribute to the understanding of the taxonomy of archaebacteria. They help in defining the differences between eubacterial and archaebacterial transcription systems. Beyond this, they yield first evidence for specificity in archaebacterial transcription. MATERIALS A N D METHODS0 rgat 1 isms T/~iwriopro/eus tenax, strain Kra 1, DSM 2078, Desiilfurococcus tn~icosiis, strain 07 and Desulfiirococcus nzobilis, strain Hvv 3. are isolated from solfataric hot springs of Iceland. T . trnus was grown as described [I]. D. ~niicosus and D. mobilis as described [2]. Siiljolobus acidocaldarius, DSM 639, was grown as reported by Brock et al. [4]. Tlzertnoplasrnn acidop / i i h z , strain 122-1B2, was kindly supplied by E. A. Freundt, Aarhus. and grown as in [9]. EnzyniesThe RNA polymerases from Luc/obacillus c i~r v u t u~...
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