Coordinated regulation of gene expression by E ... - Jacobs University

INTRODUCTION
UP element
-35 -10
Spacer
17bp
Discriminator
+1 start
Core promoter
Figure 2: Structure of consensus Eσ 70 promoter showing functionally important regions.
It is now generally accepted that promoter structure and geometry is used by
bacteria as a key regulatory element [Perez-Martin et al., 1997]. Computational studies
on promoter sequences have corroborated the experimental findings that the promoter
regions are more curved and less stable than the average genomic DNA. Observation by
Ozoline et al., of the positioning of the highly deformable TA dinucleotide
approximately every 5.6 bp, also indicate the distinct flexibility of the promoters
[Ozoline et al., 1999]. Analysis of curvature and deformability of the promoters based
on their predicted sigma (σ) factor preference also demonstrate variability. From Figure
3, it is evident that the σ 54 class promoters are less deformable compared to σ 70 class.
Sigma 54 protein is known to be structurally unrelated to σ 70 , and it also utilizes a
different pathway to form open complexes during transcription initiation, which in the
case of σ54 requires ATP [Gruber et al., 2003]. It is thought, that the core promoter -35
& -10 hexamer sequences, the discriminator sequence and the spacer region also have
evolved to posses regulatory potential. Molecular genetic examinations of stable RNA
promoters in E.coli have attributed some of the important regulatory events, like
stringent regulation and growth-phase regulation to the core promoter elements [Travers
et al., 1980; Josaitis et al., 1995; Auner et al., 2003].
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