Matrix attachment regions and methods for use thereof

A method for transfecting a eukaryotic cell to incorporate a desired gene or portion thereof into said cell wherein the method comprises co-transfecting the cell with unlinked vectors, said unlinked vectors comprising:

• a first vector comprising a first promoter and a first heterologous gene encoding the desired gene or portion thereof under the transcriptional control of the first promoter, and on first chromatin element, a second unlinked vector comprising a second chromatin element;
• and a third vector comprising a third vector comprising a second promoter and a second heterologous gene, wherein the chromatin elements are selected from the group consisting of boundary elements, matrix attachment regions, locus control regions and universal chromatin opening elements.