Contacts between Escherichia coli RNA polymerase and an early promoter of phage T7.

Specific contacts between the Escherichia coli RNA polymerase (nucleosidetriphosphate:RNA nucleotidyl-transferase, EC2.7.7.6) and the phosphates and purine bases of the A3 promoter of phage T7 cluster into three regions located approximately 10, 16, and 35 base pairs before RNA initiation site. Two of these contain nucleotide sequences that are fairly conserved among many promoters, known as the "Pribnow box" and "-35 region" homologies; the third, just upstream from the Pribnow box, is not conserved. The polymerase binds preferentially to the coding strand and for the most part touches only one face of the DNA helix.