Figure 1

Scheme of a construction of multiple chromosomal modifications, using the combined λ Red-Int/Xis system. A) Selective marker M flanked by attL _λ /attR _λ is used for introduction of an appropriate mutation into the chromosome by λ Red-dependent recombination. Then the marker is eliminated from the chromosome by λ Int/Xis site-specific recombination. As a result, only the 31 bp long attB _λ sequence linked to the mutation remains in the chromosome. Selective marker M can then be used in the next step of the introduction of multiple chromosomal modifications. B) The sequence of the attB _λ site. One of the six ORFs provided by this sequence does not contain stop codons. Hence, it is possible to design an "in-frame" deletion of a gene. Asterisks mark stop codons.