Figure 1.

Principle of pSAM2 SSR system and examples of its application (schematic representations not to scale). The SSR system requires cis-acting elements (attL and attR sites) and trans-acting elements (xis and int genes). First, the att sites are introduced in the genome via homologous recombination. The attL and attR sites are integrated in the genome by (1) a double event of homologous recombination in which the target is replaced by an excisable cassette/marker; or (2) two single events of homologous recombination after which the target is flanked by the att sites. Then the xis and int genes are introduced and temporarily expressed to perform the excision of the region flanked by attL-attR sites.