Bacterial RNA polymerases: structural and functional relationships.

The essential role of DNA-dependent RNA polymerases in gene expression and the fact that the multimeric species are highly conserved throughout nature makes these enzymes a particular fascinating area of study. Here we shall review the conservation of structures and their relationship to function, especially in the multimeric eubacterial RNA polymerases, paying particular attention to the β core subunit and to recent studies of σ-factors of both the σ (70) and σ (54) families. We shall conclude with a brief consideration of phage-encoded RNA polymerases and phage-mediated modification of the host enzyme, and of the evolution of RNA-synthesising enzymes.