The E. coli σ⁷⁰ promoter has two conserved hexamers: 5′-TATAAT-3′ centred at the −10 region and 5′-TTGACA-3′ at the −35 region, with an optimal spacer of 17 nucleotides between them. Strong promoters closely match these consensus sequences. The −10 region is involved in strand separation (melting), while the −35 region is the initial RNA polymerase recognition site.