Rifampin and rpoB mutations can alter DNA supercoiling in Escherichia coli

Two cases are described which indicate that RNA polymerase could alter DNA supercoiling. One occurred in a topA mutant in which abnormally high levels of plasmid supercoiling were lowered by rifampin, an inhibitor of the beta subunit of RNA polymerase. The second case involves suppression of a temperature-sensitive gyrB mutation by a rifampin-resistant allele of rpoB, the gene encoding the beta subunit of RNA polymerase. Measurements of chromosomal DNA supercoiling show that the rpoB mutation reduced DNA relaxation.