Identification and localization of a gene that specifies production of Escherichia coli DNA topoisomerase I.

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Abstract
A gene that specifies production of E. coli DNA topoisomerase I (.omega. protein) was identified with the aid of a radioimmunoassay for this protein. E. coli DNA topoisomerase I was produced by Salmonella typhimurium merodiploids that harbored E. coli plasmid F'' 123, but not by strains that lost this plasmid. Analysis of strains with spontaneous deletions of F''-123 showed that the gene, topA, required for production of the E. coli .omega. protein was between the trp operon and cysB gene. Deletions that eliminated topA also eliminated the supX gene. The topA gene is probably the structural gene of E. coli DNA topoisomerase I and topA is probably identical to supX.