Effect of mutations in the RNA polymerase gene and that of the transcription termination factor rho on expression of the Escherichia coli galactose operon with an IS2 polar insertion.

We analysed the effects on the expression of the gal operon of six phenotypically different mutations in the Escherichia coli RNA polymerase genes in combination with wild-type, rho, and mutant, rho15, alleles of the gene for the transcription termination factor. RNA polymerase mutations can enhance (rpoB268) or reduce (rpoB255), rpoC3, rpoB265) termination by the rho15 factor at the IS2 terminator. The rpoC1 mutation enhances the transcription of the gal operon regardless of the IS2 insertion or the rho15 mutation. Thus RNA polymerase mutations can, independently, or in combination with the rho mutation, compensate for the IS-induced, specifically IS2-induced, termination, leading to a partial restoration of gene activity.