Bases immediate upstream of the TATAAT box of the sigma 70 promoter of Escherichia coli significantly influence the activity of a model promoter by altering the bending angle of DNA

•Reports on contribution of spacer bases towards activity of Sigma 70 promoter are anomalous.•Randomisation of 3 bases immediate upstream of TATAAT resulted in 50 fold variation in activity.•These 3 bases act as whole block, not each base in particular position individually.•Several pairs of promoters have similar activities and similar structures, even though the 3 bases are very different.•Good correlation exists between bending angle of promoter DNA and promoter activity.