Organization of the Ribosomal RNA Genes in Treponema phagedenis and Treponema pallidum

Abstract

The genomic DNA fragment which contains ribosomal RNA (rRNA) genes for Treponema phagedenis was cloned into bacteriophage vector lambda EMBL3. A restriction map of the fragment was constructed and the organization of the rRNA genes was determined. The fragment contained at least one copy of the 16S, 23S and 5S sequences and the genes are arranged in the order 16S-23S-5S . Southern hybridization using radiolabeled rRNA gene probes to genomic DNA from T . phagedenis strain Reiter and T. pallidum strain Nichols showed that these organisms have two radioactive fragments which hybridize to the probes in their genome . These results suggest that both pathogenic and non-pathogenic strains of Treponema may carry at least two sets of rRNA genes on their chromosomes.We are interested in studying the organization and regulation of the genes coding for the ribosomal RNAs (rRNA) of spirochetes. Our interest in rRNA genes in spirochetes has arisen because the organization of rRNA genes for leptospires is unique (5). In addition, our finding of a functional promoter immediately preceding one operon comprising only the 5S rRNA gene gave further evidence that the other rRNA genes of the strains of leptospires are organized in separate transcription units. By the transcriptional analysis of the 5' regions of the 16S and 23S rRNA genes for Leptospira interrogans, primary transcripts were detected and the sequence resembling a promoter was seen at upstream from the 5'-terminus of the gene in each case.Organization and transcription of genes for rRNA have been highly conserved among procaryotes because the synthesis of rRNA is an essential process in the growth of any organism (13,14). In most eubacterial species so far examined, the sequences for the three rRNAs are closely linked in gene sets , in the order 16S-23S-5S (11). Some exceptions to this rule have been reported . In Thermus thermophilus (21), 16S and 23S rRNA genes are separated; in Mycoplasma gallisepticum (2), the 16S gene is separated from the other genes; and in another Mycoplasma strain (20), the 161

Physical map of the Treponema denticola circular chromosome

“…From our data, it can be derived that there are two copies of each of the rRNA genes on the chromosome of T. denticola. The hybridization patterns suggest that the genes may be closely linked, which is in agreement with the results found for Treponema phagedenis (14). A fragment cloned from this organism showed the arrangement to be rrs-rrl-rrf.…”

Physical and genetic map of the Serpulina hyodysenteriae B78T chromosome

“…Although spirochetes have a monophyletic origin (26,37) (8). A single rRNA locus is found in most Borrelia spp., with rrs separated from rrl and rrf by a small segment of DNA (-4 kb) (10,29).…”

The 23S/5S ribosomal RNA genes (rrl/rrf) are separate from the 16S ribosomal RNA gene (rrs) in Borrelia burgdorferi, the aetiological agent of Lyme disease

“…In one of the rRNA gene sets for T. phagedenis strain Reiter, three rRNA genes are arranged in the order rrsrrl-rrf (Fukunaga et al, 1992). The sequences corresponding to the three rRNAs are all contained in a 5.3 kb fragment, implying that the three rRNA genes are closely linked.…”