Nucleic Acids Research Advance Access published online on October 11, 2007
Nucleic Acids Research, doi:10.1093/nar/gkm837
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Nucleic Acid Enzymes |
Regulatory circuit based on autogenous activation-repression: roles of C-boxes and spacer sequences in control of the PvuII restriction-modification system
1Department of Medical Microbiology and Immunology, 2Program in Bioinformatics and Proteomics/Genomics, University of Toledo Health Sciences Campus, Toledo, OH 43614-2598, USA and 3Department of Microbiology, University of Gdansk, Gdansk, 80-822, Poland
* To whom correspondence should be addressed. Tel: +1 419 383 5422; Fax: +1 419 383 3002; Email: robert.blumenthal{at}utoledo.edu
Received July 30, 2007. Revised September 24, 2007. Accepted September 25, 2007.
Type II restriction-modification (R-M) systems comprise a restriction endonuclease (REase) and a protective methyltransferase (MTase). After R-M genes enter a new cell, MTase must appear before REase or the chromosome will be cleaved. PvuII and some other R-M systems achieve this delay by cotranscribing the REase gene with the gene for an autogenous transcription activator (the controlling or ‘C’ protein C.PvuII). This study reveals, through in vivo titration, that C.PvuII is not only an activator but also a repressor for its own gene. In other systems, this type of circuit can result in oscillatory behavior. Despite the use of identical, symmetrical C protein-binding sequences (C-boxes) in the left and right operators, C.PvuII showed higher in vitro affinity for OL than for OR, implicating the spacer sequences in this difference. Mutational analysis associated the repression with OR, which overlaps the promoter –35 hexamer but is otherwise dispensable for activation. A nonrepressing mutant exhibited poor establishment in new cells. Comparing promoter-operator regions from PvuII and 29 R-M systems controlled by C proteins revealed that the most-highly conserved sequence is the tetranucleotide spacer separating OL from OR. Any changes in that spacer reduced the stability of C.PvuII-operator complexes and abolished activation.
Present address: Preeti Rajesh, Department of Basic Pharmaceutical Sciences, University of South Carolina, Columbia, SC 29208, USA.
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