A genetic element that increases the frequency of gene amplification.

A repetitive mammalian genetic element, HSAG-1, has been shown to promote the amplification of the vector, pSV2-DHFR, containing the functional cDNA for dihydrofolate reductase (DHFR). LR-73 cells, a line of Chinese hamster ovary cells, were transfected with this recombinant construct or with the parent vector, then subjected to culture in selective medium containing steadily increasing concentrations of methotrexate, a drug which specifically inhibits DHFR. Cultures transfected with the HSAG-1-containing construct acquired drug resistance faster than those transfected with the parent vector. This acceleration of acquisition of drug resistance was due to an increased probability of the generation and subsequent selection of cellular variants with increased copy numbers of the vector. The effect has also been observed in CHO(DHFR-) and HeLa cell lines. Possible mechanisms for the effect of the HSAG-1 element on gene amplification are discussed.