**4.4 Preparation of induced electrocompetent cells**

Electrocompetent cells are prepared by inoculation of 50 ml LB plus appropriate reagent to select for the BAC clone of interest at 1:50 dilution from an overnight culture. Cells are incubated at 30C until the culture achieve**s** an OD600 of 0.50, which is usually 3-4 hrs. Cells are then divided into two aliquots, one for induction of lambda phage proteins and one uninduced control.

To induce the lambda phage proteins, cells are incubated at 42C for 15 minutes, and then harvested by centrifugation at 5000xg for 15 minutes at 4C. Cells are then washed 3 times in 25ml ice-cold 0.2µm-filtered ddH2O containing 10% glycerol, resuspended in 30µl 10% glycerol in ddH2O, and then transferred to cooled cuvettes for electroporation.
