DNA sequence elements located immediately upstream of the -10 hexamer in Escherichia coli promoters: a systematic study (original) (raw)

We have made a systematic study of how the activity of an Escherichia coli promoter is affected by the base sequence immediately upstream of the-10 hexamer. Starting with an activator-independent promoter, with a 17 bp spacing between the-10 and-35 hexamer elements, we constructed derivatives with all possible combinations of bases at positions-15 and-14. Promoter activity is greatest when the 'non-template' strand carries T and G at positions-15 and-14, respectively. Promoter activity can be further enhanced by a second T and G at positions-17 and-16, respectively, immediately upstream of the first 'TG motif'. Our results show that the base sequence of the DNA segment upstream of the-10 hexamer can make a significant contribution to promoter strength. Using published collections of characterised E.coli promoters, we have studied the frequency of occurrence of 'TG motifs' upstream of the promoters'-10 elements. We conclude that correctly placed 'TG motifs' are found at over 20% of E.coli promoters.