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Effects of DNA supercoiling and topoisomerases on the expression of genes coding for F165₁, a P-like fimbriae

Tessier, Marie-Catherine, Graveline, Richard, Crost, Cécile, Desabrais, Julie Annick, Martin, Christine, Drolet, Marc, Harel, Josée
FEMS microbiology letters 2007 v.277 no.1 pp. 28-36
DNA topoisomerase, DNA topoisomerase (ATP-hydrolysing), Escherichia coli, fimbriae, gene expression, intergenic DNA, mutants, mutation, operon, septicemia, swine, transcription (genetics)
Pathogenic Escherichia coli 4787 (O115:KV165) causes septicemia in pigs and expresses the fimbriae F165₁ encoded by the foo operon that belongs to the P fimbrial family. fooI and fooB, encoding specific foo regulators, are divergently transcribed; their intergenic region is responsible for the regulation of foo expression. The role of global and local supercoiling (transcription-induced supercoiling within the intergenic region) on the regulation of foo expression was investigated. Expression of fooB was significantly altered when global negative supercoiling was reduced by a mutation that decreases DNA gyrase activity. Deletion of the topA gene, encoding for topoisomerase I that relaxes local negative supercoiling, further reduced fooB expression. This suggests that both global and local supercoiling can significantly affect fooB expression. Moreover, FooI, a positive regulator of fooB expression, has no effect on fooB expression in the topA null mutant. This study showed that divergent transcription from a strong promoter can significantly enhance fooB expression and compensate for the absence of FooI in a wild-type strain.