EUBACTERIAL SIGMA-FACTORS

The initiation of transcription is the most important step for gene re gulation in eubacteria. To initiate transcription, RNA polymerase has to associate with a small protein, known as a sigma-factor. The sigma- factor directs RNA polymerase to a specific class of promoter sequence s. Most bacterial species synthesize several different sigma-factors t hat recognize different consensus sequences. This variety in sigma-fac tors provides bacteria with the opportunity to maintain basal gene exp ression as well as for regulation of gene expression in response to al tered environmental or developmental signals. This review focuses on t he function, regulation and distribution of the 14 different classes o f sigma-factors that are presently known. (C) 1998 Federation of Europ ean Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.