Hybridization of cloned ribosomal sequences to RI-restricted genomic deoxyribonucleic acids of eight species and strains of the genus produced multiband patterns consistent with the presence of 9 to 11 operons per genome. The basic structure of the repeating ribosomal gene set is highly conserved with the exception of one internalRI site located near the abutment region between the 16S and 23S ribosomal ribonucleic acid determinants. In each of the species studied, there are two abutment regions that differ in size by 0.2 kilobase; the larger region contains genes for isoleucine and alanine transfer ribonucleic acids at one-third the proportion of the smaller region. The occurrence of the RI site in strains of and gave rise upon cleavage to 1.2- and 1.4-kilobase abutment families. The absence of the RI site in , and resulted in the emergence of 1.9- and 2.1-kilobase abutment families. Mixtures of the two types of families were not found in the genomes studied.


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