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Hybridization of cloned ribosomal sequences to EcoRI-restricted genomic deoxyribonucleic acids of eight species and strains of the genus Bacillus 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 internalEcoRI site located near the abutment region between the 16S and 23S ribosomal ribonucleic acid determinants. In each of the Bacillus 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 EcoRI site in strains of Bacillus subtilis and Bacillus licheniformis gave rise upon cleavage to 1.2- and 1.4-kilobase abutment families. The absence of the EcoRI site in Bacillus globigii, Bacillus pumilus, and Bacillus amyloliquefaciens 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 Bacillus genomes studied.
Gottlieb et al. (Mon,) studied this question.