Reevaluation of the promoter structure of the class 3 flagellar operons ofEscherichia coli and Salmonella

Flagellar class 3 operons of Escherichia coli and Salmonella are transcribe d by RNA polymerase containing sigma(28). The consensus sequence of the sig ma(28)-dependent promoters was believed to be TAAA N-15 GCCGATAA. In this s tudy, we found that the E. coli genome contains a large number of sequences homologous to this consensus. However, we showed that they do not always e xert a sigma(28)-dependent promoter activity. We compare more carefully the sequences of the class 3 flagellar promoters and propose a revised structu re of the sigma(28)-dependent promoters as TAAAGTTT N-11 GCCGATAA.