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S ribosomal ribonucleic acid gene from the extreme thermophile eubacterium Thermus thermophilus HB8 has been cloned in pBR322, and the nucleotide sequence of region D has been determined, which encompasses 873 nucleotides at the 3'-end of the RNA. We compare the primary and secondary structure of this region with the respective part of the 23 S rRNA from Escherichia coli and Bacillus stearothermophilus. A high level of structural conservation can be observed, throughout the RNA domain, albeit the usage of G/C basepairs is substantial even in comparison with another thermophilic eubacterium B. stearothermophilus.It is surprising that, in contrast to the usage of 3'U-GS', the occurrence of 3'G-Us is comparable in E. coli as well as in B. stearothermophilus and T. thermophilus. Furthermore, it is most remarkable that the use of 3'A-Us and 3'U-As is, compared to E. coli, only slightly reduced in B. stearothermophilus, but drastically decreased in T. thermophilus.23 S rRNA; 23 S rRNA structure; rDNA, (Thermus thermophilus HB8)

We examined the extremely thermophilic Gram‐negative eubacterium Thermus aquaticus for the presence of plasmid DNA, and detected 5 species. The sizes were determined by electron microscopy and gel electrophoresis. The plasmids, pTA 1‐pTA 5, were of respective length: 13.5, 12.4, 11.2, 9.6 and 8.3 kb. Clones were isolated which differed in plasmid distribution. No correlation could be observed between the phenotype or growth behaviour and the presence of plasmids. The function of the plasmid structures still needs to be elucidated.

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