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RNA Polymerase—An Overview

Michael J. Chamberlin


Transcription of genetic sequences is mediated by DNA-dependent RNA polymerase. The enzyme catalyzes the initiation, elongation and termination of polyribonucleotide chains employing ribonucleoside triphosphates as substrates. The synthetic reaction shows an absolute requirement for a divalent metal ion and normally requires the presence of DNA or a polydeoxyribonucleotide to serve as a template in the reaction.

Incorporation of nucleotidyl residues from ribonucleoside triphosphates into an RNA-like material was first reported in 1959 by Weiss and Gladstone in a nuclear system from rat liver (see also Weiss, this volume). The bacterial enzyme was identified in several laboratories shortly thereafter and was shown to be DNA-dependent. Bacterial RNA polymerase was subsequently purified from a number of bacterial species, including, initially, Escherichia coli, Microccus luteus and Azotobacter vinelandii. The enzyme from E. coli has been the one most extensively studied, although the RNA polymerases of other bacteria, including species of Azotobacter, Bacillus, Pseudomonas and Caulobacter, have also been well characterized. DNA-dependent RNA polymerase has been found in all bacterial species where it has been sought, and its distribution, together with its sensitivity to drugs that inhibit bacterial transcription, indicates that it is the enzyme responsible for the major part of RNA synthesis in the bacterial cell. A newly reported bacterial RNA polymerase, the dnaG gene product, which is not related to the classic enzyme, seems to be involved in initiation of DNA synthesis for certain replicons (Kornberg, this volume); however, this enzyme is not known to play a role in general transcription.

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