Protein switches identified from diverse insertion libraries created using S1 nuclease digestion of supercoiled-form plasmid DNA |
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Authors: | Tullman Jennifer Guntas Gurkan Dumont Matthew Ostermeier Marc |
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Affiliation: | Department of Chemical and Biomolecular Engineering, Johns Hopkins University, 3400N. Charles St., Baltimore, Maryland 21218, USA. |
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Abstract: | We demonstrate that S1 nuclease converts supercoiled plasmid DNA to unit-length, linear dsDNA through the creation of a single, double-stranded break in a plasmid molecule. These double-stranded breaks occur not only in the origin of replication near inverted repeats but also at a wide variety of locations throughout the plasmid. S1 nuclease exhibits this activity under conditions typically employed for the nuclease's single-stranded nuclease activity. Thus, S1 nuclease digestion of plasmid DNA, unlike analogous digestion with DNaseI, effectively halts after the first double-stranded break. This property makes easier the construction of large domain insertion libraries in which the goal is to insert linear DNA at a variety of locations throughout a plasmid. We used this property to create a library in which a circularly permuted TEM1 β-lactamase gene was inserted throughout a plasmid containing the gene encoding Escherichia coli ribose binding protein. Gene fusions that encode allosteric switch proteins in which ribose modulates β-lactamase catalytic activity were isolated from this library using a combination of a genetic selection and a screen. |
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Keywords: | S1 nuclease protein engineering directed evolution protein switch |
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