The tdcE gene in Escherichia coli strain W3110 is separated from the rest of the tdc operon by insertion of IS5 elements

Unlike other Escherichia coli K-12 strains, W3110 contains multiple copies of the insertion sequence IS5. Some of these IS5 elements have been involve d in tandem duplication of a portion of the chromosome which includes, amon st others, the tdcABCDEFG operon genes. The nucleotide sequence and inserti on site of one of these elements, IS5P, was determined. It was shown that I S5P has inserted within the coding sequence of the tdcA gene and is flanked , not by the remaining portion of the tdcA gene, but by the extreme 3' end of the tdcD gene. In other E. coli K-12 strains the tdcD gene and three oth er genes, tdcE, tdcF and tdcG, all form part of the tdc operon. Our results demonstrate that during the duplication event the tdcABCgenes have been am plified and separated from the remaining genes tdcE, tdcF and tdcG of the o peron, which are each present in single copy.