Regulation of rrn Genes in Gram Positive Bacteria

We focus on regulation of gene expression in gram positive bacteria, using a wide range of in vivo and in vitro techniques. We use ribosomal RNA (rrn) promoters as model promoters to study how nutritional environment affects promoter activity.

In a nutritionally rich environment, the cell needs lots of protein to build new structures, and, ultimatelly, divide itself. Proteins are made at ribosomes, macromolecular structures composed of catalytic RNA and protein, which has mainly structural function. To increase protein production, the cell has to increase the number of ribosomes. It is achieved by an increased activity of rrn promoters, where rRNA transcription initiates.

Most of  the current knowledge about regulation of rrn promoters comes from the gram negative bacterium Escherichia coli. Our studies on Bacillus subtilis indicate that regulation or rrn promoters in gram positive organisms may significantly differ from gram negative bacteria (Fig.1)(Krasny and Gourse, 2004).

Fig.1. Schematic diagram illustrating mechanisms contributing to rrn P1 promoter activity in E. coli versus B. subtilis. The transcription factor Fis and RNAP CTD binding to UP element DNA account for the unusually high activity of rrn P1 promoters from E. coli, but not B. subtilis. Changing NTP and ppGpp concentrations regulate rRNA promoter activities in both bacteria, but in B. subtilis ppGpp may inhibit rRNA transcription indirectly by reducing GTP levels. For the sake of simplicity (and since its effect on B. subtilis rRNA promoters was not examined), H-NS is not pictured.

Current projects include

(i) studies of the DNA sequence elements of B. subtilis rrn promoters that determine their regulation,

(ii) studies of trans factors that affect transcription initiation at B. subtilis rrn promoters, and

(iii) studies of effects of the identity of +1 NTP on regulation of various promoters.

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