Bradyrhizobium japonicum contains only a single rRNA (rrn) gene region, despite its comparatively large genome size of 8,700 kb. The nucleotide sequence revealed an organization of rRNA and tRNA genes that is frequently found in bacteria: 5'-rrs (16S rRNA)-ileT (tRNA(Ile))-alaT (tRNA(Ala))-rrl (23S rRNA)-rrf (5S rRNA)-3'. The 5' end of the primary transcript, one of the 16S rRNA processing sites, and the 5' end of the mature 16S rRNA were determined by primer extension. DNA hybridization experiments showed that the slowly growing Bradyrhizobium strains generally have only a single copy of the 16S rRNA gene, whereas the faster-growing Rhizobium species contain three rrs copies.