We have compiled and aligned the DNA sequences of 554 promoter regions from Escherichia coli and analysed the alignment for sequence similarities. We have focused on the similarities and differences between promoters that either do or do not contain an extended -10 element. The distribution of -10 and -35 hexamer element sequences, the range of spacer lengths between these elements and the frequencies of occurrence of different nucleotides, dinucleotides and trinucleotides were investigated. Extended -10 promoters, which contain a 5'-TG-3' element, tend to have longer spacer lengths than promoters that do not. They also tend to show fewer matches to the consensus -35 hexamer element and contain short runs of T residues in the spacer region. We have shown experimentally that the extended -10 5'-TG-3' motif contributes to promoter activity at seven different promoters. The importance of the motif at different promoters is dependent on the sequence of other promoter elements.