An antibody VH domain with a lox-Cre site integrated into its coding region: bacterial recombination within a single polypeptide chain.

Bacterial lox-Cre recombination within a single antibody VH domain was achieved through integration of a loxP site into its coding sequence. The 5' half of the VH gene, in which the H2 loop was replaced by a mutant loxP site, was fused to geneIII in an 'acceptor' fd-phage vector containing also a wild type loxP site. With a 'donor' plasmid vector harbouring the 3' half of the VH gene flanked by the same, differing loxP sites it recombined into a full-length VH with the loxP site-H2 loop. This VH was purified from bacterial periplasm, where it folded into a typical immunoglobulin domain. The system allows the generation of large VH repertoires using lox-Cre recombination.