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pubmed:abstractText |
DNA sequences upstream of the rrnB P1 core promoter (-10, -35 region) increase transcription more than 300-fold in vivo and in vitro. This stimulation results from a cis-acting DNA sequence, the UP element, which interacts directly with the alpha subunit of RNA polymerase, increasing transcription about 30-fold, and from a positively acting transcription factor, FIS, which increases expression another 10-fold. A DNA region exhibiting a high degree of intrinsic curvature has been observed upstream of the rrnB P1 core promoter and has thus been often cited as an example of the effect of bending on transcription. However, the precise position of the curvature has not been determined. We address here whether this bend is in fact related to activation of rRNA transcription. Electrophoretic analyses were used to localize the major bend in the rrnB P1 upstream region to position approximately -100 with respect to the transcription initiation site. Since most of the effect of upstream sequences on transcription results from DNA between the -35 hexamer and position -88, i.e. downstream of the bend center, these studies indicate that the curvature leading to the unusual electrophoretic behavior of the upstream region does not play a major role in activation of rRNA transcription. Minor deviations from normal electrophoretic behavior were associated with the region just upstream of the -35 hexamer and could conceivably influence interactions between the UP element and the alpha subunit of RNA polymerase.
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