sentences:  In some cases the presence of a recombinase enzyme and the recombination sites is sufficient for the reaction to proceed; in other systems a number of accessory proteins and/or accessory sites are required.Many different genome modification strategies, among these recombinase-mediated cassette exchange (RMCE), an advanced approach for the targeted introduction of transcription units into predetermined genomic loci, rely on SSRs.Site-specific recombination systems are highly specific, fast, and efficient, even when faced with complex eukaryotic genomes.