On the use of double FLP recognition targets (FRTs) in the LTR of retroviruses for the construction of high producer cell lines.

A pilot experiment for the construction of a hamster derived, high producer cell line using site specific recombination is described. In the experiment chromosomal loci with intrinsic high expression characteristics were sought via infection with a retroviral construct, containing double FRT sites and subsequent screening for overproduction of an encoded markergene. These sites were then targeted with a second vector, that recombined via the FLP/FRT system from Saccharomyces cerevisiae yielding cells that had the second construct at exactly the same position as the first. By using retroviral vectors with double and single FRT sites, respectively, stable clones can be created that can no longer be excised with FLP.