Abstract: The present invention concerns the use of a nucleic acid fragment comprising a portion of at least 100 contigous nucleotide bases which portion has a sequence the same as, or homologous to a portion of corresponding length of the sequence as set out in SEQ ID NO:1 starting at nucleotide approximately 1 and ending at nucleotide approximately 16879 or the same as, or homologous to a portion of the corresponding length of the sequence complementary to said SEQ ID NO: 1 within the specified positions, for improving the persistence of transfected cells expressing one or more gene(s) of interest operably linked to said acid nucleic fragment. The invention also relates to an expression cassette for the expression of one or more gene(s) of interest which expression is controlled by one or more control sequence(s) and a nucleic acid fragment as defined above.