Regulatory Subunits of RNA Polymerase

Abstract

INTRODUCTION
The discovery that the σ subunit of RNA polymerase governs site selection suggested a new model for the positive control of gene transcription. It was proposed by Burgess et al. (1969) that σ polypeptide could be replaced by regulatory proteins that would bind to the bacterial transcriptase and enable core enzyme to initiate transcription at new promoter sites. Reports of alterations in the transcriptional specificity of RNA polymerase in phage-infected (Seifert et al. 1969; Bautz and Dunn 1969; Travers 1969) and sporulating (Losick and Sonenshein 1969) bacteria generated considerable interest in this idea. Only recently, however, has it been possible to isolate purified RNA polymerases that contain known regulatory proteins and that direct specific gene transcription in vitro. Here we will review recent studies of regulatory subunits of RNA polymerase induced by phages T4, SPO1 and SP82, as well as several RNA polymerase binding proteins for which a transcriptional function has not yet been assigned.

IDENTIFICATION OF RNA POLYMERASE BINDING PROTEINS
The techniques of immunoprecipitation and affinity chromatography have made it possible to identify proteins that interact with RNA polymerase in crude extracts of bacteria and bacteriophage-infected cells. Proteins that bind to RNA polymerase can be precipitated by antibody directed against purified polymerase (see, for example, Greenleaf, Linn and Losick 1973) and will adhere to polymerase immobilized on agarose (Ratner 1974a). Ultimately, however, the identification of a new subunit of RNA polymerase requires the purification to homogeneity of the polymerase-subunit complex by conventional purification procedures and reconstitution of the...