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J Mol Biol. 2000 Jun 16;299(4):859-64.

The G+C-rich discriminator region of the tyrT promoter antagonises the formation of stable preinitiation complexes.

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Unité de Physicochimie des Macromolécules Biologiques, Institut Pasteur, CNRS URA 1773, Paris, 75724, France.


RNA polymerase forms a highly stable preinitiation complex at many prokaryotic promoters in the absence of ribonucleotides. These are often characterised by the longevity of the DNA strand-separated (open) complex in the presence of heparin. In contrast, such complexes are notoriously unstable at the promoters for rRNA and tRNA under similar conditions. The high G+C content within the DNA-melting region of these promoters has been implicated in this seemingly anomalous behaviour. Here, we used rapid-pulse UV laser photo-footprinting to monitor the transient structural intermediates formed at the Escherichia coli tyrT promoter. Promoter derivatives with A+T for G/C base substitutions within the G+C-rich discriminator region (-7 to -1) augmented the stability of complexes on both linear fragments and supercoiled plasmid DNA. Analysis of the lifetime of the preinitiation complexes as a function of the discriminator sequence reveals a direct relationship between the A+T content of the DNA-melting region and the stability of the ensuing complex. Our results are consistent with the premise that a G/C block to DNA-untwisting and/or DNA-melting operates to prevent the formation of the stable isomers that are implicated in most other transcription initiation pathways.

[Indexed for MEDLINE]

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