THE ESCHERICHIA-COLI CYSG PROMOTER BELONGS TO THE EXTENDED - 10 CLASSOF BACTERIAL PROMOTERS

The Escherichia coli cysG promoter has been subcloned and shown to fun ction constitutively in a range of different growth conditions. Point mutations identify the - 10 hexamer and an important 5'-TGN-3' motif i mmediately upstream. The effects of different deletions suggest that s pecific sequences in the -35 region are not essential for the activity of this promoter in vivo. This conclusion was confirmed by in vitro r un-off transcription assays. The DNAase I footprint of RNA polymerase at the cysG promoter reveals extended protection upstream of the trans cript start, and studies with potassium permanganate as a probe sugges t that the upstream region is distorted in open complexes. Taken toget her, the results show that the cysG promoter belongs to the 'extended - 10' class of promoters, and the base sequence is similar to that of the P1 promoter of the E. coli galactose operon, another promoter in t his class. In vivo, messenger initiated at the cysG promoter appears t o be processed by cleavage at a site 41 bases downstream from the tran script start point.