In order to create a system in which two independent plasmids can be integrated into a mycobacterial chromosome, a mycobacterial plasmid was constructed containing the phage attachment site attP from the mycobacteriophage L5 genome and additionally containing the bacterial attachment site, attB. This plasmid will integrate into the mycobacterial chromosome via recombination of the plasmid-borne attP site with the chromosomal attB site in the presence of a mycobacterial vector carrying the L5 integrase (int) gene. The integrated plasmid has a plasmid-borne attB site that is preserved and will accept the integration of additional mycobacterial plasmids containing the L5 attP site. This system should be useful in the construction of novel mycobacterial strains. In particular, this system provides a method by which several recombinant antigens or reporter constructs can be sequentially inserted into a mycobacterial strain and subsequently tested.
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