ISSN:
1365-2958
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Biology
,
Medicine
Notes:
The antigen 43 surface protein of Escherichia coli is expressed in a phase-variable manner by a mechanism involving alternative activation and repression of transcription of the agn43 gene. The repressor is the OxyR DNA-binding protein, and its binding site was found to be located downstream of the agn43 transcription start site in a region of DNA that encompasses three 5′-GATC-3′ sequences that are subject to Dam-mediated DNA methylation. It has been suggested previously that the phase-variable expression of antigen 43 results from a competition between Dam methylase and the OxyR repressor for these sites. The 5′-GATC-3′ sequences were inactivated for methylation by site-directed mutagenesis, and all possible combinations of inactive and active sites were assessed for effects on phase-variable expression of the agn43 gene. Inactivation of any 5′-GATC-3′ site individually had no effect; at least two sites had to be inactivated to disrupt the normal pattern of expression. Studies of OxyR interaction with agn43 DNA showed that methylation of any two 5′-GATC-3′ sites was necessary and sufficient to block binding of the repressor. It was also found that the adenines of the second and third 5′-GATC-3′ sites are required for OxyR binding, demonstrating that the sites for Dam methylation and for repressor binding are intimately associated. This is consistent with a competition model in which Dam and OxyR share a preference for specific DNA sequences in the regulatory region of the agn43 gene.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1046/j.1365-2958.2002.02905.x
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