Analysis of in vivo RNA transcription products of the ilvGEDA attenuator region of Escherichia coli K12.

The precise points of in vivo transcription initiation and termination in the leader region of the ilvGEDA operon of Escherichia coli K12 have been determined. Leader RNA transcription products from either side of the attenuator have been identified and quantitated by T1 fingerprint analyses under growth conditions which affect operon expression. The results provide in vivo confirmation of the ilvGEDA attenuation model. Previous DNA sequence and in vitro transcription analyses have demonstrated that this operon is preceded by two strong in vitro promotors. The studies reported here show that transcription is initiated in vivo only from the downstream promotor and that no detectable in vivo expression from the upstream promotor is observed under conditions which affect operon regulation.