Localization of RNA polymerase binding sites on T7 DNA

Abstract

Binding sites on T7 + DNA for Escherichia coli RNA polymerase have been positioned by a combination of techniques involving: (1) protection by RNA polymerase at known Hind II sites, and (2) binding studies with T7 + DNA predigested with Hind II. A single small T7 Hind II fragment of 80 nucleotide pairs is retained on a nitrocellulose filter as a binary complex with RNA polymerase holoenzyme from among complete Hind II digestion mixtures of T7 + DNA. This binding site appears analogous to the T7 A2 promoter. The binding sites corresponding to the A1 and A3 promoters are effectively destroyed by the action of Hind II. RNA polymerase specifically blocks the action of Hind II at two loci on T7 + DNA, both of which have been positioned by mapping techniques. Evidence suggests these are analogous to the A1 and A3 promoters. Two additional weak but specific RNA polymerase DNA binding sites have also been positioned on the T7 genome.