Involvement of the transcription start site of the rnpB promoter in generating stringent signals in Escherichia coli

Abstract

Transcription from the P- l promoter of the E. coli rnpB gene encoding a stable RNA, MI RNA, is repressed upon the stringent response. The GC-rich discriminator region (positions -7 to -1) between the -10 region and the transcription start site is known to be responsible for this transcription repression. Since transcription from the rnpB promoter starts at the G nucleotide, the +1 start site may be involved in generating stringent signals. In this study, we generated various promoter variants, from which transcription started with G or A, by introducing mutations at positions -1 and/or +1. The transcription site was shifted to one nucleotide upstream when the C nucleotide at position -1 was changed to G or A. Therefore, we were able to obtain another set of the promoter variants carrying the 6-bp discriminator region, in addition to a set of the promoter variants having the normal 7-bp discriminator region. The stringent response of these promoter variants was examined. The results indicate that the GC pair at the transcription start site is also involved in generating stringent signals like the GC pairs in the discriminator region. The stability of initiation complexes of the promoter variants was also examined. Promoter variants having A at the +1 site, which should less stringent repression, form more stable initiation complexes than promoter variants having G at the +1 site.