Because of its small size, the landing pad is easily recombineered into the desired location in the genome [8 ] by λ-Red mediated homologous recombination, and serves as a subsequent target for cleavage by I-SceI and recombination by λ-Red. Successful integration of the landing pad can be positively selected for through growth on medium containing tetracycline (for tetA landing pad) or galactose as the sole carbon source (for galK landing pad).