Effect of DNA superhelicity on transcription termination.

Restriction fragments containing either leut (a rho-independent transcription termination site) and/or leut' (a rho-dependent transcription termination site) were cloned into plasmid pOL4. Treatment of plasmid-containing Escherichia coli strains with coumermycin resulted in loss of in vivo plasmid superhelicity 10 min after antibiotic addition. Galactokinase levels specified by these plasmid-containing strains were the same regardless of whether functional DNA gyrase was present. These results suggest that transcription termination is unaffected by the superhelical state of DNA.