Genetic Analysis of Template Specificity of RNA Polymerases (Gene 1 Products) Coded by Phage T3 × T7 Recombinants within Gene 1

Abstract

INTRODUCTION
The RNA polymerase coded by gene 1 of bacteriophage T7 is a single peptide chain protein with a molecular weight of about 107,000; it is highly specific for promoters located within the “late” region of the T7 genome and it will not appreciably transcribe the DNAs of Escherichia coli, or of the phages T2 or λ, for instance (Chamberlin and Ring 1973). However, this polymerase may use as a template the DNA of a T7 relative, phage T3, although at an efficiency of only about 50% as compared to T7 DNA (Dunn, Bautz and Bautz 1971; Chamberlin and Ring 1973). On the other hand, the T3 gene 1 RNA polymerase may use T7 DNA as a template at only about 15% the efficiency with which it uses T3 DNA (Dunn, Bautz and Bautz 1971). The reasons for these differences in template specificity are not fully understood. Different affinities of the polymerases for T7- and T3-specific promoters and terminators may be involved. In fact, Golomb and Chamberlin (1974a, b) have shown that the T7 RNA polymerase synthesizes only one species of RNA from a T3 DNA template, whereas it synthesizes seven RNA species from T7 DNA. This was interpreted by these authors as due to the existence of different types of promoters located in the “late” region of the T3 DNA; all these promoters would be recognized by the T3 RNA polymerase, but only one of them would be recognized by the corresponding T7 enzyme. In any event, the different...