I-Ceul recognition sites in the rrn operons of the Bacillus subtilis 168 chromosome: inherent landmarks for genome analysis

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Abstract
The Bacillus subtilis 168 circular chromosome yielded ten fragments on I-Ceui endonuclease digestion. I-Ceul recognizes a 26 bp sequence that is located within the gene encoding the 235 subunit of the rRNA in Chlamydomonas eugametos, Escherichia coli and Salmonella typhimurium. The precise locations of the I-Ceul sites of the B. subtilis chromosome were determined on a Notl-Sfil physical map by (i) double digestion analyses with I-Ceul and Sfil, (ii)comparison of mutant strains lacking a specific rrn operon, (iii)using an I-Ceul linking clone and (iv) analysis of nucleotide sequence data of some rrn operons. In conclusion, all the I-Ceul sites were located within the B. subtilis rrn operons and the I-Ceul sites were conserved in all the B. subtilis 168 derivatives tested. Thus, variations in size of the I-Ceul fragments must be due to genome alterations. A B. subtilis 168 strain was investigated with I-Ceul. We demonstrated that the aberrant structure was the outcome of the inversion of an ~ 1700 kb DNA segment.