IGEM:Caltech/2007/Protocols/Recombineering Protocol

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iGEM 2007

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This protocol is adopted almost verbatim from the Oppenheim et al, 2004. Recombineering. The strains used for recombineering carry a defective E prophage containing the pL operon under control of the temperature-sensitive repressor cI857. 1. The strain of choice is grown in a shaking water bath at 32C in LB with 0.4% maltose to mid-exponential phase, A600 0.4–0.6 (30 ml is adequate for several recombineering reactions). The culture is harvested by centrifugation and resuspended in 1 ml TM (10mM Tris base, 10mM MgSO4, pH 7.4). The phage to be engineered is added at a multiplicity of infection of 1–3 phages/cell (we assume cell density of approximately 10^8/ml before concentration) and allowed to adsorb at room temperature for 15 min (this step would need modification for other phages, i.e., adsorption on ice). Meanwhile, two flasks with 5-ml broth are pre warmed to 32C and 42C in separate shaking water baths. The infected culture is divided and half inoculated into each flask; the cultures are incubated an additional 15 min. The 42C heat pulse induces prophage functions; the 32C uninduced culture is a control. After induction, the flasks are well chilled in an ice water bath and the cells transferred to chilled 35-ml centrifuge tubes and harvested by centrifugation at approximately 6500g for 7 min. The cells are washed once with 30-ml ice-cold sterile water; the pellet is quickly resuspended in 1-ml ice-cold sterile water and pelleted briefly (30 s) in a refrigerated microfuge. The pellet is resuspended in 200-\mu l cold sterile water and 50–100 Al aliquots are used for electroporation with 100–150 ng PCR product or 10–100 ng oligonucleotide. We use a BioRad E. coli Gene Pulser set at 1.8 mVand 0.1-cm cuvettes. Electroporated cells are diluted into 5 ml 39jC LB medium and incubated to allow completion of the lytic cycle. The resulting phage lysate is diluted and titered on appropriate bacteria to obtain single plaques (for more details, see Thomason et al., 2003). Oligonucleotides. The oligonucleotides were purchased from Invitrogen without additional purification. The purified oligonuclotide was subjected to electrophoresis in a 15% PAGE-Urea gel, excised from the gel without direct UV irradiation and eluted using the Elutrap electro-separation system (Schleicher and Schuell). The size-purified oligonucleotide was then precipitated with isopropanol, washed with ethanol, dried, and stored at �20jC.