The authors compiled and analyzed the DNA sequences of 168 promoter regions (-50 to +10) for Escherichia coli RNA polymerase. The promoters were categorized into two groups based on whether they were defined by genetic or biochemical criteria. A consensus promoter sequence was determined based on homologies among 112 well-defined promoters, which showed substantial agreement with previous compilations. Additionally, 98 promoter mutations were tabulated, with most altered base pairs conforming to a general rule: down-mutations decrease homology and up-mutations increase homology to the consensus sequence. The study highlights the importance of conserved sequence elements in promoter function and supports the use of genetic and biochemical criteria for defining promoters.The authors compiled and analyzed the DNA sequences of 168 promoter regions (-50 to +10) for Escherichia coli RNA polymerase. The promoters were categorized into two groups based on whether they were defined by genetic or biochemical criteria. A consensus promoter sequence was determined based on homologies among 112 well-defined promoters, which showed substantial agreement with previous compilations. Additionally, 98 promoter mutations were tabulated, with most altered base pairs conforming to a general rule: down-mutations decrease homology and up-mutations increase homology to the consensus sequence. The study highlights the importance of conserved sequence elements in promoter function and supports the use of genetic and biochemical criteria for defining promoters.