Abstract: Described are various embodiments of specific sequences for recombinant gene insertion, amplification and expression in the genomes of a variety of mammalian cells are disclosed. A DNA vector containing one or more such sequence enables high levels of recombinant gene expression following transfection, stable integration and amplification. The selection and cloning of the specific loci and the expression of recombinant genes is disclosed, as are the DNA vectors and the host cells.

Abstract: The invention provides for a system for uploading genes of interest into an artificial chromosome expression system (ACE) that has been engineered to include multiple sites for site-specific, recombination directed integration, whereby a second or further gene of interest can be loaded onto the ACE by a targeting vector, through the acceptor recombination site(s) on said ACE.