The NusA and NusG proteins of Escherichia coli increase the in vitro readthrough frequency of a transcriptional attenuator preceding the gene for the beta subunit of RNA polymerase.

The genes for the beta (rpoB) and beta' (rpoC) subunits of Escherichia coli RNA polymerase are the distal members of a complex transcriptional unit that contains four upstream ribosomal protein genes. The RNA polymerase subunit genes are transcribed at a lower frequency than the ribosomal protein genes as a result of termination at an attenuator preceding rpoB. A purified in vitro transcription system was developed using linear DNA templates that carry the attenuator. The ability of known termination and antitermination proteins to modulate termination at the attenuator was tested. Both NusA and NusG increase the frequency of transcriptional readthrough at the attenuator whereas NusB, S10, and Rho had no significant effect in this system.