Transcriptional termination at a fully rho-independent site in Escherichia coli is prevented by uninterrupted translation of the nascent RNA.

We have examined the possibility that translation reading through a fully rho-independent transcriptional terminator in Escherichia coli might prevent termination, as already established for rho-dependent terminators. Plasmids were constructed with and without interposition of the rho-independent coliphage T7 'early' terminator between a promoter and galK. Our constructions ensured either that there was no upstream translation, or that translation (initiated at the galE ribosome binding site) stopped upstream of, or at the normal position (the T7 gene 1.3 stop codon) with respect to, the transcriptional terminator; or else downstream of both this stop codon and the terminator. Our galactokinase enzyme and mRNA measurements on strains harbouring these plasmids indicate that 'readthrough translation' eliminates transcriptional termination at the T7 site. This effect is suppressed if the rate of ribosome movement is reduced with fusidic acid.