| Summary: | <p>Abstract</p> <p>Background</p> <p>Introducing point mutations into bacterial chromosomes is important for further progress in studies relying on functional genomics, systems- and synthetic biology, and for metabolic engineering. For many investigations, chromosomal systems are required rather than artificial plasmid based systems.</p> <p>Results</p> <p>Here we describe the introduction of a single point mutation into the <it>Escherichia coli </it>chromosome by site-directed mutagenesis without leaving any selection marker. We used Red<sup>®</sup>/ET<sup>® </sup>Recombination in combination with <it>rpsL </it>counter-selection to introduce a single point mutation into the <it>E. coli </it>MG1655 genome, one of the widely used bacterial model strains in systems biology. The method we present is rapid and highly efficient. Since single-stranded synthetic oligonucleotides can be used for recombination, any chromosomal modification can be designed.</p> <p>Conclusion</p> <p>Chromosomal modifications performed by <it>rpsL </it>counter-selection may also be used for other bacteria that contain an <it>rpsL </it>homologue, since Red<sup>®</sup>/ET<sup>® </sup>Recombination has been applied to several enteric bacteria before.</p>
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