CLONING THE RIBOSOMAL-RNA OPERONS OF MYCOPLASMA-FLOCCULARE AND COMPARISON WITH THOSE OF MYCOPLASMA-HYOPNEUMONIAE

In contrast to other mycoplasma species the 16S/23S rRNA and 5S rRNA o perons of Mycoplasma flocculare and Mycoplasma hyopneumoniae map at le ast 150 kb apart (20% of the genome). Both operons from M. flocculare have been cloned and sequenced. The 23S rRNA gene sequence showed 96.7 % homology with the corresponding gene of M. hyopneumoniae, equalling that found earlier for 16S rRNA and confirming the close phylogenetic relationships of these organisms. A possible upstream promoter was ide ntified. Sequence elements upstream and downstream from each structura l gene could form a stem needed for maturation of the immature rRNA tr anscript to mature 16S and 23S rRNA. We also identified two possible s tem-and-loop sequences 3' to the 23S rRNA gene. The 5S rRNA gene itsel f also showed high homology with the corresponding structural gene of M. hyopneumoniae, although the upstream and downstream sequences were highly heterologous.