Flp-In Flips Out

Anyone who's ever made stable cell lines knows that clones can vary wildly in terms of expression levels. Some express the transfected gene at high levels, some express at low levels, and some, for whatever reason, fail to express at all. Individual clones must, therefore, be carefully screened. And, because integration sites are random, direct comparison of multiple clones can be uncertain.

In 1999 Invitrogen of Carlsbad, Calif., unveiled its Flp-In™ recombinase-based system as a solution to these problems, says Kerry Lowrie, product manager of mammalian gene-expression products. Recently, the company upgraded the product line, adding new plasmids and cell lines.

The system uses Flp recombinase¹ to insert any sequence into a specific genomic location. Flp catalyzes recombination between two FRT elements; if one is genomic and the other extrachromosomal, the plasmid-borne sequence will be integrated into the genome. "The Flp-In system really eliminates all of the time...