STATISTICAL EXAMINATION OF DISSIMILARITY OF PROMOTER AND PROMOTER-LIKE SEQUENCES IN ESCHERICHIA COLI

Abstract

Specificity of Escherichia coil σ⁷⁰-promoter consensus-like sequences is examined by the x²-statistics. The promoter consensus bases are serially designated as T₁ T₂, G₃, A₄ C₅, A₆, T₇, A₈, T₉ A₁₀., A₁₁ and T₁₂ by neglecting a spacer bases between A₆ and T₇. Occurrences of highly conserved sequences of the consensus are investigated with 75 transcription units in E. coli. About four-fifths of transcription units involving all of the polycistronic units in E. coli genome are repressed in both strands, A remarkable difference is detected on the frequencies of T₁., T₇ and T₁₂ between in promoters and coding regions. That is, whereas for promoter region they are higher than the critical frequency, for coding region they are lower, especially for 17-base spacers, than the critical one. The facts that occurrences of highly conserved sequences are repressed in transcription units and that x-distribution of the three T's(T₁, T₇ and T₁₂) are complementary between in promoters and coding regions suggest that transcription initiations within transcription units are repressed and the three T's of promoter sequences constitute a transcription trigger.