Purification and Physical Properties of E. coli RNA Polymerase

INTRODUCTION The purpose of this review is to present a summary of (1) the variables involved in the purification of E. coli DNA-dependent RNA polymerase (E.C. 2.7.7.6), (2) the criteria by which the purity of the enzyme can be assessed, and (3) the physical properties of the enzyme and its subunits. It is hoped that this will provide a useful guide to choosing a purification method and a reference for the properties of the enzyme. No attempt will be made to be all-inclusive or historical, but rather the most recent and thorough studies will be emphasized. Several reviews covering similar material have appeared (Richardson 1969; Geiduschek and Haselkorn 1969; Burgess 1971; Chamberlin 1974a, b). This review will deal with RNA polymerase holoenzyme, core polymerase and sigma factor. Holoenzyme has the subunit composition α 2 ββ ′ σ and can be resolved into two components: core enzyme ( α 2 ββ ′) and sigma factor ( σ ). Most researchers have studied a mixture of holoenzyme and core polymerase. Holoenzyme appears to be involved in the synthesis of most cellular RNA, with the possible exception of certain RNA primers involved in DNA replication, as discussed by Kornberg (this volume). A variety of other forms of RNA polymerase have been reported and in some cases, named: polymerase II found in stationary cells (Chao and Speyer 1973); holoenzyme II found in small amounts and consisting of core enzyme and a polypeptide termed σ ′ (Fukuda, Iwakura and Ishihama 1974); a series of activities in crude extracts with different sedimentation properties and template activities (Snyder...