Ribosomal RNA genes in bacteria: evidence for the nature of the physical linkage between 16S and 23S RNA genes in Bacillus subtilis.

The nature of the arrangement of 16S and 23S ribosomal RNA genes on the Bacillus subtilis chromosome was studied by means of a Cs(2)SO(4) density gradient centrifugation technique after complexing DNA-(ribosomal) RNA hybrids with mercuric ions. It was observed that the same fragments of single-stranded DNA with an average molecular weight of 1.9 x 10(6) which hybridize with 23S RNA also hybridize with 16S RNA. This indicates that genes for both these species of ribosomal RNA are physically linked on such DNA fragments. Some evidence suggests that the two types of genes are interspersed with each other, perhaps in sets, each of which contains a 16S and a 23S ribosomal RNA gene.