Abstract
In bacterial promoters subject to stringent control the heptanucleotide sequence spanning nucleotide positions -5 to +2 (defining the -10 region [D. Pribnow, J. Mol. Biol. 99:419-443, 1975] as positions -12 to -6) is highly conserved. This conserved region, for which the best consensus sequence is [Formula: see text] is absent from promoters which are not under stringent control.