Organization of the regions flanking the rRNA cistrons of Mycoplasma strain PG50.

Four clones harboring fragments of the rRNA cistrons have been isolated from a genomic library of Mycoplasma PG50 DNA. By heteroduplex and displacement loop analysis, supplemented with sequence data, we demonstrate that the four clones together cover the two rRNA cistrons of Mycoplasma PG50 as well as the flanking regions. Parts of the cloned fragments have been analyzed in detail, and the following conclusions have been reached. Genes for tRNALys and tRNALeu are located about 450 bp upstream of the 16S rRNA gene of rrnA. An open reading frame of at least 215 codons is located just upstream of and in the same direction as rrnB. Analysis of the 3' flanking region of rrnA reveals that no tRNA genes succeed this operon. Also here an open reading frame can be identified, which is at least 83 codons long and has a putative promoter and a possible ribosome binding site. Its direction is the same as that of rrnA. None of the open reading frames has any function assigned yet. The last 880 bp of the 23S and the 5S genes of rrnA are compared with the corresponding Bacillus subtilis sequence and sequences of other Mycoplasma species, respectively.