Pausing of RNA polymerase during in vitro transcription through the ilvB and ilvGEDA attenuator regions of Escherichia coli K12.

Synchronized single-round transcriptions, in vitro, from templates encoding the leader RNA of the ilvB and ilvGEDA operons result in the accumulation of a transcript consistent with RNA polymerase pausing after the 1:2 stem that could form in each of the leader RNAs. Addition of L-factor or guanosine 5'-diphosphate,3-diphosphate extended the pause half-life obtained with the ilvB template; addition of L-factor and guanosine 5'-diphosphate,3'-diphosphate together had an additive effect on the pause half-life. L-factor also extended the pause half-life of the pause obtained with the ilvGEDA template; however, addition of guanosine 5'-diphosphate,3'-diphosphate did not. The results obtained are consistent with the model for attenuation proposed by Yanofsky et al. (Yanofsky, C., Das, A., Fisher, R., Kolter, R., and Berlin, V. (1984) UCLA Symposium of Gene Expression (Hamer, D., and Rosenberg, M., eds) pp. 295-310, Alan R. Liss, Inc., New York) in which transcriptional pausing after the synthesis of the 1:2 stem-loop closely couples transcription and translation of the leader region.