Evidence for rifampicin-promoted readthrough of a fully rho-dependent transcriptional terminator.

We have previously presented evidence that rifampicin promotes readthrough of various transcriptional terminators in vivo. This conclusion was based on measurements of galactokinase or beta-galactosidase synthesis in Escherichia coli strains, harbouring plasmids having the terminators fused upstream of galK or lacZ respectively. The terminators tested did not include any known example of a fully rho-dependent signal. We now show that the drug does stimulate galactokinase production when galK is fused downstream of such a terminator: the first rightward terminator of lambda. We also show that the nusA1 host mutation affects neither termination nor the drug response at this site.