CHARACTERIZATION OF THE UNLINKED 16S RDNA AND 23S-5S RIBOSOMAL-RNA OPERON OF WOLBACHIA-PIPIENTIS, A PROKARYOTIC PARASITE OF INSECT GONADS

The rRNA-encoding genes (rDNAs) have been cloned and characterized fro m Wolbachia pipientis (Wp), the gonadial bacteria-like parasite of the mosquito Culex pipiens (Cp) and the moth Ephestia cautella (Ec). In W p from both insect species the rDNAs are organized in a way which appe ars to be very unusual. The rRNAs are encoded by two unlinked transcri ption units, each present in a single copy per genome. One contains th e 16S rDNA only, while the other is an operon encoding both the 23S an d 5S rDNAs. Each transcription unit contains two putative upstream pro moters, and downstream a Rho-independent terminator. The 16S rDNA, as well as the 23S-5S rRNA operon are not linked to any tRNA-encoding seq uence and lack the antitermination boxes which are usually present imm ediately downstream from eubacterial promoters of rDNAs. Wp infecting Ec and Cp are highly similar taking as criteria the rDNAs and their fl anking sequences. However, it clearly appears that each insect species harbours a different and specific Wp strain, or even subspecies. Phyl ogenetic relationships deduced from the complete sequences of their rD NAs undoubtedly confirm that Wp from Cp and Ec belong to the alpha-gro up of Proteobacteria, and are closely related to the Rickettsia.